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Composite Structures
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  • Determination of the in-plane shear modulus of unidirectional carbon
           fiber-reinforced plastics using digital image correlation and
           finite-element analysis
    • Abstract: Publication date: 1 December 2019Source: Composite Structures, Volume 229Author(s): Jae-Hyuk Choi, Jinhyeok Jang, Wonbo Shim, Jeong-Min Cho, Sang-Jae Yoon, Chi-Hoon Choi, Heung Nam Han, Woong-Ryeol Yu Accurate in-plane shear properties are essential to simulate the mechanical behavior of fiber-reinforced laminated composites. Herein, a digital image correlation technique was used to analyze unidirectional carbon fiber-reinforced composites by three shear-test methods (±45° in-plane, Iosipescu, and V-notched rail shear tests), focusing on the uniformity of shear deformation during each test. The V-notched rail shear test imposed the most uniform shear deformation. This test, however, still imposed non-uniformity around the deformation regime for the in-plane shear modulus calculation, which needed to be accommodated. The non-uniformity was virtually characterized by a combination of various material properties using finite-element analysis. A universal correction factor of 0.925 resolved the non-uniformity involved in the V-notched rail shear test. This enabled the in-plane shear modulus of unidirectional carbon fiber- or glass fiber-reinforced composites to be accurately determined.
  • A novel understanding of the normalized fatigue delamination model for
           composite multidirectional laminates
    • Abstract: Publication date: 1 December 2019Source: Composite Structures, Volume 229Author(s): Yu Gong, Wangchang Li, Hao Liu, Suzhen Yuan, Zhangming Wu, Chuanzeng Zhang Normalized fatigue delamination models have been widely applied by researchers in the characterization of the fatigue delamination behavior of composite laminates. However, the inherent mechanism of this normalization method has not been explored. This study aims to present a physical understanding on the normalized fatigue delamination model from a viewpoint of energy. The fatigue delamination behavior is considered to be governed by the driving force and delamination resistance, and based on this principle the physical mechanism of the fatigue delamination is studied. A new physics-based normalized fatigue delamination model is proposed in this paper. In order to experimentally validate the proposed fatigue delamination model, mode I fatigue delamination tests are performed on double cantilever beam specimens to obtain the experimental data with different amounts of the fiber bridging. The results show that the normalized model is suitable to accurately characterize the fatigue delamination behavior of the composite laminates by using a single master curve. The master curve is finally employed as a standard approach to predict the fatigue results. Good agreement between the predicted and the experimental results is achieved, therefore it approves the applicability of the proposed fatigue delamination model in characterizing the fatigue delamination growth behavior.
  • Study on the torsion behavior of 3-D braided composite shafts
    • Abstract: Publication date: 1 December 2019Source: Composite Structures, Volume 229Author(s): Wenfeng Hao, Zhen Huang, Lu Zhang, Guoqi Zhao, Ying Luo The structural parameters of three-dimensional (3-D) braided composites have important influence on their mechanical properties. The torsional properties of the 3-D braided composite shafts with braiding angles of 25°, 35° and 45° were tested by MTS809. Based on the micro-structure of 3-D braided composite material, unit cell model was established, and the failure process of 3-D braided composite transmission shaft under torsion was studied by finite element method. The results show that the shear resistance of the specimens increases with the increase of braiding angle, and the specimens still have a certain bearing capacity after unloading. The simulation results show that the damage of the specimens first appears at the fiber/matrix interface. With the increase of load, the damage of the matrix expands and connects between the interfaces, and finally leads to the failure of the specimens. The failure of small braiding angle specimens is mainly caused by the accumulation of matrix damage, while the fiber damage of large braiding angle specimens increases, and the deformation is more consistent with the experimental results.
  • Damage detection based on vibration for composite sandwich panels with
           truss core
    • Abstract: Publication date: 1 December 2019Source: Composite Structures, Volume 229Author(s): Jie Zhou, Zheng Li Composite sandwich panels with truss core have been widely studied for their outstanding characteristics and excellent designable properties, but very little of this work was focused on non-destructive testing (NDT) methods. Based on mode curvatures and a two-dimensional (2D) continuous wavelet transform (CWT), a baseline-free NDT method is proposed for damage identification in these types of sandwich panels. Initially, the 2D CWT is applied to process the mode curvatures from specific mode shapes. Then, considering the structural periodicity of the truss, which is a distinctive characteristic of these sandwich panels, a novel damage index is defined through a combination of the structural periodicity and the coefficients of the CWT. Numerical simulations and experimental tests were conducted to identify damage in the composite sandwich panels with core trusses forming a pyramidal lattice. Results show that the proposed method is efficient and reliable, and has a good resolution in identifying one or more truss bars missing detection without a baseline and thus has the potential in damage detection of composite sandwich panels.
  • Recurrence quantitative analysis for porosity characterization of CFRP
           with complex void morphology
    • Abstract: Publication date: 1 December 2019Source: Composite Structures, Volume 229Author(s): S.J. Jin, X.C. He, J. Chen, S.Q. Shi, L. Lin The porosity characterization of Carbon Fibre Reinforced Plastics (CFRP) by ultrasonic attenuation measurement is restricted when the back-wall echoes are weak or absent at high porosity, and the estimation accuracy is decreased with increment of porosity due to complex void morphology. In this paper, Real Morphology Void Models (RMVMs) with different porosity were established to simulate the interaction between ultrasonic waves and voids with complex morphology. Subsequently, Recurrence Quantification Analysis (RQA) was introduced to process ultrasonic backscattered signals generated by voids so as to present Recurrence Plots (RPs) for porosity characterization. Recurrence Rate (RR) was selected as RQA variable to quantitatively analyze RPs, avoiding the determination of additional parameters. The correlation between porosity P and RR was revealed by simulation for the first time, and verified by experiments with CFRP laminates having porosity of 0.8%–4.2%. The complex and random void morphology induced the non-mapping relationship between P and RR, influencing estimation accuracy of porosity. The normalized results indicated that porosity characterization with RR was less affected by void morphology for P > 1.97% in comparison with ultrasonic attenuation measurement. It is concluded that RQA is valuable for porosity characterization of CFRP with high porosity and strong attenuation.
  • Experimental investigation of shear capacity and damage analysis of
    • Abstract: Publication date: 1 December 2019Source: Composite Structures, Volume 229Author(s): Lokman Gemi, Ceyhun Aksoylu, Şakir Yazman, Yasin Onuralp Özkılıç, Musa Hakan Arslan Prefabricated structures supported with purlins are exposed to numerous damages due to the excessive snow loadings as vertical loadings. The thinned regions of the purlins are responsible with the failure of the structure since the shear cracks usually initiate at these regions and propagate along with the purlins, and as a result, a total collapse may occur. In this study, carbon fiber reinforced polymer (CFRP) composites with four different configurations (P2–P5) were employed for strengthening prefabricated purlins in order to increase the strength of the purlin against shear damage generated under vertical loading. The load carrying capacities and damage patterns of the purlins were compared. The failure of the reference purlin (P1) was occurred as a shear damage at the thinned regions before reaching its bending capacity. However, the failure characteristic of the CFRP reinforced purlins was dominated by the bending damage and the vertical loading capacity of the purlins were increased up to 59% depends on the CFRP wrapping. Damage analysis of the CFRP composite was also performed. Various damage modes of the structure such as cover separation, air voids, delamination, debonding, fiber bundles breakage, matrix cracks, fiber bundles debonding, fiber breakage and buckling were observed and explained thoroughly.
  • Seismic retrofitting of rectangular bridge piers using ultra-high
           performance fiber reinforced concrete jackets
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): Teng Tong, Siqi Yuan, Weiding Zhuo, Zhiqi He, Zhao Liu An innovative seismic retrofitting technique for “as-built” reinforced concrete (RC) bridge piers was proposed, by using ultra-high performance fiber reinforced concrete (UHPFRC) jackets. One “as-built” and two UHPFRC jacket-retrofitted rectangular cross-section RC piers were fabricated and cyclically loaded. Damage evolutions, skeleton curves, strength and stiffness degradations, ductility, self-centering and energy dissipation capacities were derived and analyzed. The two jackets mitigated the concrete damage and enhanced the self-centering capacity of a RC pier. The 850 mm-height jacket significantly increased the strength, but ductility and cumulative energy dissipation capacity. On the other aspect, the 400 mm-height jacket exhibited superior performances in ductility and cumulative energy dissipation capacity. Three strengthening mechanisms were brought by a UHPFRC jacket, and they were cross-section enlargement effect, gap opening effect, and passive confinement effect. Among them, formulas for the confinement effect are analytically obtained. The fiber-based finite element (FE) model for the UHPFRC jacket-retrofitted RC pier is developed within OpenSees framework. The simulation agrees well with the experimental results and can benefit further researches involved in the seismic retrofitting with a UHPFRC jacket.
  • Analytical and experimental study of the ultimate strength of delaminated
           composite laminates under compressive loading
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): N. Kharghani, C. Guedes Soares An improved and efficient analytical solution is proposed to predict the behaviour and the ultimate strength of composite laminates containing delamination. For this purpose, a Layerwise Higher order Shear Deformation Theory based on polynomial shape functions using Rayleigh–Ritz approximation technique are utilized. The ultimate strength and initial stages of propagation of the delaminated zone are determined using fracture analysis. The results demonstrate continuous functions to calculate in-plane and out-of-plane displacements, rotations, strains, stresses, energy and load carrying capacity under in-plane compressive loading. Moreover, a significant experimental investigation has been carried out for specimens with cross-ply stacking sequence and various material properties, geometries, delamination type and boundary conditions. The experimental study includes fabrication process, tensile tests to determine material properties and buckling test of the defected specimens.
  • Hyperelastic characteristics of graphene natural rubber composites and
           reinforcement and toughening mechanisms at multi-scale
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): Chen Xue, Hanyang Gao, Yuchen Hu, Guoxin Hu In order to meet the increasing demand of damping and shock absorption materials, graphene-based rubber composites are considered as a candidate material because of their excellent strength and toughness. Here, we propose a small and excessive amount of 3-aminopropyl triethoxy silane (APTS) modified graphene oxide as a functional composite material for filling and reinforcing natural rubber, and we also prepare the corresponding natural rubber composites containing graphene oxide (go) and reduced graphene oxide (rgo). Compared with natural rubber filled with carbon black, the crosslinking density and mechanical properties of the composites containing graphene prepared in this paper improved significantly. The strengthening and toughening mechanism of APTS modified graphene oxide filled composites revealed at the micron, nano and even molecular level by FTIR, AFM and SEM characterisation. Notably, by comparing the surface RMS roughness of graphene oxide edited with a small and excessive amount of APTS, we find that the higher the surface roughness of graphene, the more obvious the effect of strengthening and toughening after compounding with natural rubber. These results will be helpful for the application of graphene composites in rubber damping materials.
  • Hygro-thermo-mechanical modelling and analysis of multilayered plates with
           embedded functionally graded material layers
    • Abstract: Publication date: Available online 17 September 2019Source: Composite StructuresAuthor(s): F. Moleiro, E. Carrera, A.J.M. Ferreira, J.N. Reddy This work addresses the modelling and analysis of multilayered plates with embedded functionally graded material (FGM) layer(s) under hygro-thermo-mechanical loadings. The hygroscopic, thermal and mechanical problems are all solved simultaneously using a new layerwise mixed model based on least-squares formulation with multi-field independent variables, namely, displacements, temperature, moisture, transverse stresses, transverse heat flux, transverse moisture flux, in-plane strains and in-plane components of both thermal and moisture gradients. This mixed formulation ensures that interlaminar C0 continuity requirements, where the material properties may actually change, are fully fulfilled a priori. An added feature is included to fully describe the FGM layer z-continuous effective properties through-thickness, using any homogenization method, by applying a high-order z-expansion to its effective properties, similarly to finite element approximations. The numerical results demonstrate the effects of hygrothermal environments in the analysis of distinct multilayered plates with embedded FGM layers, considering different side-to-thickness ratios, under a series of hygro-thermo-mechanical loadings. The rule of mixtures is used to estimate the FGM layer effective properties, including different material gradation profiles. Three-dimensional (3D) approximate solutions corroborate this model’s capability to predict accurately a quasi-3D hygro-thermo-mechanical description of the through-thickness distributions of displacements and stresses, temperature and heat flux, moisture and moisture flux.
  • A novel elastoplastic constitutive model for woven oxide/oxide ceramic
           matrix composites with anisotropic hardening
    • Abstract: Publication date: Available online 17 September 2019Source: Composite StructuresAuthor(s): Hui Liu, Zhengmao Yang, Huang Yuan The oxide/oxide ceramic matrix composite exhibits superior mechanical properties in high temperature environment. However, complex nonlinear behavior is not clarified for high performance applications. The present work developed an elastoplastic constitutive model considering variations of hardening behavior over the stress states by introducing a novel loading function. The model can account for heterogeneous initial yield and complex hardening behavior accurately and was verified from experiments under tension and compression conditions with various off-axis angles. The computational results agree with stress-strain responses containing softening up to failure under arbitrary in-plane loading conditions.
  • Numerical analysis of drop impact-induced damage of a composite fuel tank
           assembly on a helicopter considering liquid sloshing
    • Abstract: Publication date: Available online 17 September 2019Source: Composite StructuresAuthor(s): Dong-Hyeop Kim, Sungchan Kim, Sang-Woo Kim The study examined the structural damage and impact behavior of a composite fuel tank assembly subjected to drop impact based on the fluid–structure interaction analysis. It was implemented using a coupled Eulerian–Lagrangian method, and the Hashin failure criteria were considered to evaluate the damaged area and tendency of the assembly for the composite failure modes. We investigated the effects of the critical parameters, namely the amount of fuel and drop impact angle, on the damage of the assembly during the drop impact. The results indicated that the failed area of the assembly became significant when the amount of liquid fuel increased, and the drop impact angle aggravated the damage on the assembly. It is expected that the findings can be utilized as guidelines for drop impact tests and for assessing the airworthiness of a composite fuel tank assembly in the future.
  • Coupled effect of temperature and impact loading on tensile strength of
           ultra-high performance fibre reinforced concrete
    • Abstract: Publication date: Available online 16 September 2019Source: Composite StructuresAuthor(s): Xiangwei Liang, Chengqing Wu, Yekai Yang, Cheng Wu, Zhongxian Li This study focused on coupled effect of temperature and impact loading on tensile strength of an ultra-high performance fibre reinforced concrete (UHPFRC), which retains 69% of its original compressive strength after exposure to 1000 °C. The relationship between tensile strength and compressive strength was investigated under the coupled action since temperature may have different effects on them. Static tests and dynamic tests using a self-designed Split Hopkinson Pressure Bar (SHPB) system were conducted at temperatures 20, 200, 400, 600 and 800 °C. Comparison was made between tensile strength and compressive strength of UHPFRC obtained in hot state and cooled-down state. It was found splitting tensile strength fell sharply beyond 400 °C but still retained 41% of its original strength at 800 °C, well above other concretes. Temperature and combined action of elevated temperature and impact loading have different effects on splitting tensile strength and compressive strength.
  • An orthotropic augmented finite element method (A-FEM) for high-fidelity
           progressive damage analyses of laminated composites
    • Abstract: Publication date: Available online 16 September 2019Source: Composite StructuresAuthor(s): Yunwei Xu, Jaedal Jung, Saeed Nojavan, Qingda Yang In this paper, we extended a recently developed augmented finite element method (A-FEM) to account for the complicated progressive damage processes in laminated composites, which are of orthotropic nature and typically develop multiple types of cracking systems including intra-ply matrix/fiber splitting, fiber rupture in tension and/or kinking in compression, and inter-ply delamination. The orthotropic A-FEM represents all of these major damage modes with improved nonlinear cohesive zone models (CZMs) that explicitly consider the asymmetric tension- and compression-responses. A rigorous verification and validation process demonstrates that the developed orthotropic A-FEM can adequately account for the initiation and propagation of various types of cracks and their coupled evolution under complex stress environments. A-FEM predictions to progressive damage processes in several multidirectional notched and un-notched laminates, including the initiation of multiple cracks and their nonlinearly coupled progression with delaminations all the way up to the final, catastrophic failure, are all in excellent agreement with experimental measurements and observations.
  • Experimental investigation on the cutting mechanism and surface generation
           in orthogonal cutting of UD-CFRP laminates
    • Abstract: Publication date: Available online 16 September 2019Source: Composite StructuresAuthor(s): Qinglong An, Chongyan Cai, Xiaojiang Cai, Ming Chen As carbon fiber reinforced polymer (CFRP) have been widely used as the main material of aeronautic load-carrying parts, there are more and more demands of relevant machining work. Due to the significant anisotropy of CFRPs, defects may easily occur in the machining process. In this paper, the mechanism of cutting and surface generation at different fiber orientations were investigated by orthogonal cutting of unidirectional carbon fiber reinforced polymer (UD-CFRP) laminates. Surface roughness, surface morphology involving fractures and defects were discussed. The results revealed that the cutting mechanism under parallel fiber cutting conditions is the interface layering separation dominated by in-plane shear stress and the machined surface is relatively flat and smooth; the cutting mechanism under perpendicular fiber cutting conditions is shear-fracture separation dominated by shear stress and the machined surface is mainly characterized by regular fiber cross fractures; the cutting mechanism includes the interface layering separation and shear-fracture separation, and the machined surface is characterized by a regular fluctuating surface composed of fiber cross fractures with fiber orientation angle 0°
  • Prognosis of Fatigue induced Stiffness Degradation in GFRPs using
           Multi-Modal NDE data
    • Abstract: Publication date: Available online 16 September 2019Source: Composite StructuresAuthor(s): Portia Banerjee, Rajendra Prasath Palanisamy, Lalita Udpa, Mahmood Haq, Yiming Deng Prediction of expected life of a composite structure especially at the initial stages of degradation is challenging owing to inherent heterogeneity and lack of robust damage growth models. This paper focuses on prognostic study of matrix stiffness degradation in glass fiber reinforced polymers (GFRP) subjected to fatigue testing using data from multi-modal nondestructive evaluation (NDE) techniques, specifically the optical transmission and guided wave sensing. Combining information from multiple sensors exploits advantages of signal complementary and hence effectively improve damage growth modeling and prediction in composites. However, matrix stiffness inferred from two independent NDE techniques varies owing to differences in their sensitivity, measurement noise or model discrepancy, often leading to inconsistent and inaccurate reliability assessment. A joint likelihood updation technique is therefore proposed in existing particle filtering (PF) framework which enables dynamic optimization of Paris-Paris model parameters at every time step by discarding noisy or biased measurements. Comparison of stiffness prediction using multi-sensor data with prognosis results on single sensor or average measurement demonstrates the benefit of joint likelihood based prediction of residual stiffness. An additional advantage of the proposed approach towards reduction of particle count in existing particle filtering framework is discussed, thereby lowering prediction time and computation resources. Overall, multi-sensor NDE and prognosis methodology is discussed for reliable assessment of fatigue life in GFRP composites structures.
  • Effects of surface contact on the dynamic responses of delaminated
           composite plates
    • Abstract: Publication date: Available online 16 September 2019Source: Composite StructuresAuthor(s): Yi He, Yi Xiao, Zhongqing Su This paper investigates the modal parameters such as the damping ratio, frequency and shape of delaminated composite plates with contact properties. The contact damping is analyzed using a viscoelastic Coulomb friction model with sliding phase, which combines energy dissipation of sliding friction and sticky friction. Finite element method (FEM) based models simulate the dynamic responses of delaminated composite plates, in which the constant normal contact stiffness and contact damping are introduced via penalty stiffness method and equivalent viscous damping, respectively. Relevant vibration experiments are set up to obtain the modal parameters of delaminated composite plates. The results show that the modal damping ratio of the composite laminated plates increases significantly with increase in the delamination percentage, and the contact damping plays a major role in the increase of the modal damping ratio. Furthermore, the contact stiffness also has a minor influence on the modal frequency and shape of delaminated composite plates. The experimental data is consistent with simulations, thereby establishing the accuracy of the FEM model.
  • In-plane crashworthiness of re-entrant hierarchical honeycombs with
           negative Poisson’s ratio
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Hailun. Tan, Z.C. He, K.X. Li, Eric Li, A.G. Cheng, Bing Xu Both auxetic structures and hierarchical honeycombs are marked with lightweight and excellent mechanical properties. Here, we combine the characteristics of auxetic structures and hierarchical honeycombs, and propose two re-entrant hierarchical honeycombs constructed by replacing the cell walls of re-entrant honeycombs with regular hexagon substructure (RHH) and equilateral triangle substructure (RHT). The honeycombs are subjected to in-plane impact in order to investigate the crashworthiness by using the commercial software LS-DYNA. The plateau stress of RHH and RHT in x and y directions are derived by a two-scale method. The results from numerical simulation indicate that the specific energy absorption of RHT and RHH is improved by up to 292% and 105%. RHT and RHH improve the mean crushing force value by 298%, 108% respectively compared with the classic re-entrant honeycomb (RH) under quasi-static loading at stress plateau region. The RHT and RHH still have the characteristic of negative Poisson’s ratio. Additionally, the parametric studies are further carried out to investigate the effects of impact velocities and relative densities on crashworthiness. All the findings of this study indicate that the proposed two hierarchical honeycombs exhibit an improved crushing performance, and RHT provides the highest energy absorption capacity among all specimens.
  • On the Progressive Failure Simulation and Experimental Validation of Fiber
           Metal Laminate Bolted Joints
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Christian Gerendt, Aamir Dean, Thorsten Mahrholz, Raimund Rolfes The joint efficiency of mechanical joints in fiber-reinforced composite materials can be increased significantly by embedding metal plies in the composite layup, as in the case of fiber metal laminates. In this work, a novel finite element-based framework is presented for predicting the static progressive failure behavior of fiber metal laminate bolted joints. Motivated from experimental observations, thaaaaae proposed framework accounts not only for damage in the fiber-reinforced composite plies, but also for different types of damage in the metallic inlays. For this purpose, user-defined continuum-damage constitutive models are formulated and employed in the general-purpose FE software Abaqus/Implicit for the fiber-reinforced polymer plies and the embedded metallic inlays. Accordingly, the interaction between different failure modes and the influence of the bolt’s washer on the damage evolution is considered to increase the fewgbe]’nbfr.g n/dddwpredictive quality. To demonstrate the applicability and validity of the developments, predictive simulations are carried out and compared to conducted experimental measurements on different fiber metal laminate grades (GFRP/stainless steel and CFRP/titanium) with a wide range of metal volume content, reaching from 0 % (pure composite material) to 50 %.
  • Discrete Element Model for ZrB2-SiC Ceramic Composite Sintering
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Vincent Iacobellis, Ali Radhi, Kamran Behdinan A combined viscoelastic/sintering model is incorporated in a sintering study of a ZrB2-SiC composite using the discrete element method. The sintering component of interacting particle forces arises from grain boundary and surface diffusion while the viscoelastic effect ensures adequate mass transport between interacting particles. The model includes a weighted transition between a Hertz-Mindlin type contact and the sintering model during heating of the discrete elements up to the sintering temperature. The model is verified by simulating pressureless sintering of zirconium diboride ceramic composites reinforced with multiple volume percentages of silicon carbide particulates. The model showed improvements in porosity, density and elastic modulus with increased particulate phase percentage up to 15wt%. The model showed enhanced densification at higher temperatures with good correlation with experimental data.
  • Impact property of TiAl3–Ti laminated composite
           fabricated from metallic sandwich
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Chatdanai Boonruang, Angkrich Theppawong TiAl3–Ti Laminated composite has been fabricated by hot pressing of titanium–aluminium sandwich in order to improve impact toughness of TiAl3. Fabrication process has been reported and structure evolution, phase portion, hardness, impact toughness, and fractography of the composite are investigated using XRD, XPS, SEM, EDS, hardness test, and impact test. The results show formation of TiAl3 and production of TiAl3–Ti laminated composite after the sandwiches have been hot pressed at 600 and 650 °C for 24 h in low vacuum system. TiAl3–Ti thickness ratio attributed to phase portion and hardness of TiAl3–Ti interface region are shown to be promoted by fabrication temperature. Fractography and EDS results can allow the impact–fracture mechanism of composite to be proposed. The impact toughness of composite can be improved by using low fabrication temperature in order to reduce TiAl3–Ti thickness ratio.
  • Detection of Fiber Waviness in CFRP Using Eddy Current Method
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Zhiwei Zeng, Jingjing Wang, Xiaohua Liu, Junming Lin, Yonghong Dai In this paper, a method of detecting fiber waviness in carbon fiber reinforced polymer (CFRP) using eddy current (EC) probe is proposed. The probe consists of a rectangular excitation coil and a rectangular reception coil that are perpendicular to each other. The excitation coil is along the designed fiber direction. Fiber waviness changes the direction of EC and generates a magnetic field component that is normal to the reception coil; thereby an output signal is obtained. The results of simulation and experiments show that the resolution of testing fiber direction using the proposed method is as small as 0.5° and fiber waviness can be detected according to the variation of scanning signal.
  • Crashworthiness and failure analysis of steeple-triggered hat-shaped
           composite structure under the axial and oblique crushing load
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Hongyong Jiang, Yiru Ren A clear understanding of failure mechanisms and coupling interaction of multiple failure modes greatly contributes to crashworthiness design of composite structure. Thus, the crashworthiness and failure of steeple-triggered hat-shaped composite structure (HSCS) is investigated based on finite element method. The stacked-shell model is adopted to capture both intra- and inter-laminar failure modes and validated with available experiments. The effect of oblique crushing on the crashworthiness of HSCS is predicted and analyzed. Further, to improve specific energy absorption (SEA), the HSCS as a sub-structure is used to design cellular structures including unit-cell, double-cell and four-cell structures. From the predicted results, failure process and complex coupling failure mechanisms of HSCS are revealed. It is found that the oblique crushing angle has a significant effect on the crashworthiness and there exists a critical angle. It is also revealed that the SEA increases with the increase of the cell number due to different splaying modes.
  • Numerical Analysis on Viscoelastic Creep Responses of Aligned Short Fiber
           Reinforced Composites
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Zhaogui Wang, Douglas E. Smith Micro-mechanics analysis using the Representative Volume Element (RVE) approach implemented with the Finite Element Method has been widely used for computing material properties of unidirectional fibrous polymer matrix composites. However, little attention has been given to viscoelastic RVEs of discontinuous fiber reinforced composites. This paper develops a RVE-based Finite Element algorithm for evaluating the effective viscoelastic creep behaviors of aligned short fiber composites. A parametric study including considerations of fiber volume fraction, fiber aspect ratio and fiber packing geometry is performed through the proposed algorithm. Computed results indicate that increasing the fiber volume fraction decreases the mechanical compliance of the overall compound, and the effect of fiber reinforcements is particularly significant in the direction of fiber alignment. Additionally, increasing the fiber aspect ratio reduces the creep compliance coefficient along the direction of fiber alignment more than coefficients along other directions. The fiber packing geometry affects the values of axial compliance properties at low fiber volume fraction and its impacts become less as the fiber volume fraction increases. We also provide an application to simulate the equivalent viscoelastic creep response out of the RVE approach through ABAQUS user defined material subroutine, and the maximum absolute error between the two sets of data is only 1%.
  • Experimental and numerical assessment of structural behaviour of laminated
           glass balustrade subjected to soft body impact
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Marcin Kozłowski Glass is a commonly used material in modern architecture not only for building enclosures, but also for glazed barriers preventing building occupants from falling out of balconies and different levels inside buildings. The main purpose of the balustrades is to transfer the imposed loads to the main structure of the building. That includes static loads related to the crowd pressure (horizontal line load applied at the top edge of the balustrade), but also dynamic actions produced by humans in motion. The latter is related to an accidental situation when a moving person accidentally hits the balustrade. The paper provides design principles and a review of existing standards regarding glass balustrades with a special emphasis on dynamic loads. It also presents results of an experimental campaign and numerical studies on the evaluation of the structural safety of fully-glazed balustrades subjected to soft-body impact. It includes experimental characterisation of the impactor and soft body impact tests on a glass balustrade in two states: intact and in post-failure state (with single glass ply damaged). The results of the numerical studies show good agreement with experiments in terms of displacement of glass balustrade, stress in glass and acceleration of the impactor.
  • Mechanical properties and self-healing capacity of eco-friendly ultra-high
           ductile fiber-reinforced slag-based composites
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Huy Hoang Nguyen, Jeong-Il Choi, Hyeong-Ki Kim, Bang Yeon Lee This paper presents an experimental investigation of the mechanical properties and an evaluation of the self-healing properties of eco-friendly ultra-high-ductile fiber-reinforced alkali-activated slag (AAS)-based composites. Based on single types of activators, optimal mixtures were designed and prepared. Compressive strength and uniaxial tension tests were performed to measure the mechanical properties of each composite mixture. In addition, a series of experiments, including self-healing observation by microscopy and stiffness recovery measured through resonant frequency, was undertaken to evaluate the self-healing capacity of alkali-activated slag-based composites. SEM/EDS analysis was utilized to visualize the healing morphology and chemical compositions of the healing materials. The test results showed that AAS-based composites achieved excellent tensile ductility, accompanied with reasonable self-healing performance. Moreover, calcium carbonate was found to be the main healing material in the case of calcium activator-based AAS composites, whereas C-(N)-A-S-H was the dominant healing product generated for sodium activator-based AAS composites. The new findings provide inspiration for an eco-friendly construction material capable of sustainability in terms of material greenness, impressive tensile behavior, and high potential self-healing property.
  • Reliability Evaluation of Carbon-Nanotube-Reinforced-Polymer Composites
           based on Multiscale Finite Element Model
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Jorge Alberto Palacios, Rajamohan Ganesan Experimental investigations to study the material behavior of nanocomposites have limitations. Hence, computational modeling and simulation encompassing multiscale material behavior provide an alternate approach to study the mechanical properties of such materials. The objective of the present work is to develop a computational framework for performing a probabilistic analysis of a Carbon-Nanotube-Reinforced-Polymer (CNRP) material by using the stress-strength model to determine the reliability and hazard associated with its mechanical properties, in terms of its longitudinal elastic modulus and ultimate longitudinal strength. A 3D multiscale finite element model of the Representative Volume Element of the nanocomposite consisting of a polymer matrix, an imperfect Single-Walled-Carbon-Nanotube (SWCN) and an imperfect interface region has been constructed for this purpose. The polymer matrix is modeled with the Mooney-Rivlin strain energy, the imperfect SWCN is modeled as a space frame structure using the Morse potential, and the interface region is modeled via van der Waals (vdW) links. In practical applications, the SWCN is not perfect, and it possesses structural defects, and moreover, the vdW links are not perfect. Such imperfections are characterized using the Monte Carlo simulation technique. The reliability and Hazard functions of the CNRP material are calculated using the Maximum Entropy Method.
  • Closed Form Solution for Free Vibrations Analysis of FGPM Thick Cylinders
           Employing FSDT under Various Boundary Conditions
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Hossein Daemi, Hamidreza Eipakchi A porous material contains a structure in which its density reduces when the volume increases due to voids. The high strength, low weight and absorption of the sound or impact convert the porous materials desirable with vast applications to different fields of science and technology. In this paper, an analytical method is proposed for investigating the vibrations behavior of thick porous cylinders for various boundary conditions. The porosity variation is function of the thickness as symmetric, asymmetric or uniform. For mathematical modeling, the first-order shear deformation theory is used as displacement field, by considering the transverse normal strain effect. Hamilton’s principle in conjunction with the linear kinematic relations and Biot constitutive equations are employed to extract the motion equations. The governing equations contain four coupled partial differential equations. These equations are solved analytically and the natural frequencies and mode shapes are determined. A parametric study is performed and the effect of the materials and mechanical properties is studied for different boundary conditions. The results are compared with the finite element methods and the available results in the literature.
  • Effect of Braiding angle on progressive failure and fracture mechanism of
           3-D five-directional carbon/epoxy braided composites under impact
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Can Cui, Jiwei Dong, Xianbiao Mao At present, there are few systematic studies on dynamic mechanical response of 3-D braided composites according to different braiding angles. In this paper, the mechanical properties, real-time progressive failure law and fracture mechanism of 3-D five-directional braided composites at different braiding angles are systematically studied by using SHPB test apparatus. The results show that braiding angle is an important factor affecting the mechanical properties of composites, which under smaller braiding angle are higher, and the longitudinal mechanical properties of composites are more sensitive to braiding angle. In particular, the material still has a certain post-peak bearing capacity after longitudinal impact, presenting a nonlinear change trend of first increasing and then decreasing. The high-speed photographs and stress-strain curves show that different braiding angles reflect the degree of progressive failure of composites, and different loading patterns reveal the morphology of progressive failure of composites. With the increase of braiding angle, the braiding structure changes greatly, which leads to gradual serious progressive failure of composites. This point is also confirmed from the perspective of macroscopic failure characteristics and microscopic fracture morphology.
  • Development of an impact damage model for medium and large scale composite
           laminates using stacked-shell modeling: Verification and Experimental
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): K.T. Fotopoulos, G.N. Lampeas, O. Flasar In the present work, the predictive capabilities of a Finite Element (FE) damage model developed for accurate and efficient analysis of medium to large scale structures are investigated. The proposed damage model is based on stacked sublaminate modeling approaches with cohesive interfaces. A pre-failure elastic response verification procedure is followed by model validation, performed by a Mode-I fracture toughness experimental campaign, from which the model predictive capabilities in interlaminar damage initiation and propagation are assessed. The analysis is then extended to the simulation of low velocity impact experiments found in the open literature, investigating the capabilities of the proposed model in intralaminar and interlaminar damage prediction. The results demonstrate the proposed methodology’s accuracy and efficiency in the simulation of laminated composites under static and impact conditions.
  • Influence of residual stresses on the buckling behaviour of thin-walled,
           composite tubes with closed cross-section – numerical and experimental
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Paweł Czapski, Tomasz Kubiak The aim of this research is to investigate the influence of residual stresses on the behaviour of thin-walled laminates during compression until failure. We investigate the compression of a squared cross–section, GFRP columns with dimensions: (width × height × thickness): 80 × 80 × 2 mm. The length of the tubes is equal to 250 mm. The material used to manufacture the specimens was eight–layered pre-preg and we analysed six combinations of angular arrangements. The autoclaving technique was employed to produce the samples. In this paper, a new FE model of tubes’ compression including residual stresses from the manufacturing process is presented. The FE model where residual stresses are not taken into account has been underestimated by the real structures’ behaviour. Therefore, the first part of the study is devoted to preparing a simplified model of the curing process, while in the second the manufacturing and curing stresses are transferred to the model of compression. Backed by experimental data, the study shows that residual stresses have a significant influence on buckling performance, which finds confirmation in the experiments.
  • Novel Filler Materials for Composite Out-of-Plane Joints
    • Abstract: Publication date: Available online 11 September 2019Source: Composite StructuresAuthor(s): Zsombor Sápi, Sam Hutchins, Richard Butler, Andrew Rhead In the manufacture of the out-of-plane joints of composite stiffened panels, such as the connection between skin and T, I, omega shaped stiffeners, a filler material is needed to fill the void between the flanges, web and skin. The most common filler is a rolled unidirectional prepreg tape (“noodle”), which is not only expensive to manufacture, but also has low strength that can lead to premature failure of the loaded joint. In this work, eight novel filler concepts are introduced and experimentally validated against the baseline noodle via T-joint tensile tests. Polyamide nonwoven interleaved joints increase the damage tolerance of the structure and nonwoven nanofibres increase the failure initiation load. 3D printed fillers have lower strength but demonstrate the possibility of thermoplastic-thermoset hybrid structures. Fillers made of chopped prepreg match the strength of the baseline noodle and can serve as a low cost replacement. Another low cost, resin infused braided concept has lower strength, but its counterpart using multiple individual braids has the same strength as the unidirectional noodle. Moreover, the latter concept shows that different resin systems can be cured together without causing a knockdown in strength, and can serve as a basis for a range of novel applications.
  • Clustering effect on mechanical properties and failure mechanism of open
           hole high modulus carbon fiber reinforced composite laminates under
    • Abstract: Publication date: Available online 10 September 2019Source: Composite StructuresAuthor(s): Xiaodong Wang, Weidong Li, Zhidong Guan, Zengshan Li, Yao Wang, Mi Zhang, Jianwen Bao, Shanyi Du The clustering effect of open hole high modulus carbon fiber (M40J) reinforced composite laminates under compressive load is studied with digital image correction (DIC), acoustic emission (AE) and high-resolution digital camera. Three types of quasi-isotropic laminates [45m/0m/-45m/90m]ns (m×n=4) with different clustering levels (m=1, 2 and 4) are manufactured and tested to investigate their mechanical properties and failure mechanism. The experimental results indicate that as clustering levels increasing, the open hole compressive strength gradually decreases accompanied by failure mode transferring from brittle fracture to delamination. Four types of sub-critical damages are found in the progressive failure process: splitting, delamination, layers buckling and layer compressive damage. The layers buckling and layer compressive damage can result in final failure of laminates yielding failure mode of delamination and brittle fracture, respectively. Besides, the effect of sub-critical damages and layer thickness on both mechanical properties and failure mode are discussed consequently obtaining the qualitative relationships between open hole compressive strength and material mechanical properties. The ratio of inter-fiber strength to layer longitudinal compressive strength is the crucial factor affecting the mechanical properties, and it should be controlled within the range where the push-in failure mode occurs for better properties.
  • Performances of Magnesium- and Steel-based 3D Fiber-Metal Laminates Under
           Various Loading Conditions
    • Abstract: Publication date: Available online 10 September 2019Source: Composite StructuresAuthor(s): Davide De Cicco, Farid Taheri The marriage of composites and metals is becoming an increasingly popular approach for obtaining resilient and lightweight materials. Our research group recently combined a 3D fiberglass/epoxy composite and thin magnesium sheets to render a significantly more effective and resilient light-weight material system. We are now interested in evaluating the feasibility of using steel as an alternative to magnesium due to the widespread use of steel in the automobile industry. Therefore, in this paper, the static buckling, impulse buckling, post-buckling, and lateral impact performances of the magnesium-based and steel-based 3D fiber-metal laminates (3D-FML) are systematically investigated and compared.
  • Hybrid fiber use on flexural behavior of ultra high performance fiber
           reinforced concrete beams
    • Abstract: Publication date: Available online 10 September 2019Source: Composite StructuresAuthor(s): Kaan Turker, Umut Hasgul, Tamer Birol, Altug Yavas, Halit Yazici In this study, the flexural behavior of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) beams produced in mono and hybrid forms were investigated experimentally and numerically. Twelve doubly reinforced concrete beams were casted with four different reinforcement ratios representing low to excessive levels. The beams were produced in three groups to study the effects of mono and hybrid steel fiber usages. The first group beams of four are non-fiber beams while the second group contains only short-straight fiber of 13 mm. The last group is composed of hybrid form where the short-straight fiber of 13 mm and the long-hooked fiber of 60 mm were blended together. The beams were subjected to four-point loading, and the parameters of deflection and curvature ductilities, flexural stiffness, flexural moment capacity, cracking behavior and compressive strain were discussed. The test results indicated that the UHPFRC beams with high reinforcement ratios above the limits in current design codes provide remarkable benefits through the fibers’ contribution. It can be deduced that the hybrid fiber usage showed better flexural performance, in general, comparing to the mono form. In addition, two numerical approaches were proposed to predict nominal moment capacity of the UHPFRC beams in the mono or hybrid form.
  • Size-effect independence of particleboard fracture toughness
    • Abstract: Publication date: Available online 10 September 2019Source: Composite StructuresAuthor(s): Daniela Scorza, Liviu Marsavina, Andrea Carpinteri, Camilla Ronchei, Sabrina Vantadori The present paper aims to prove the size-effect independence of particleboard (PB) fracture toughness when the Modified Two-Parameter Model (MTPM), recently proposed by some of the present authors, is used to measure such a parameter. Firstly, three-point bending (TPB) tests on single-edge notched specimens characterised by three different values of thickness are performed for a commercial particleboard. By exploiting such experimental data, the value of the fracture toughness is analytically determined through the MTPM. Then, a fracture toughness index is defined by taking into account the dependence of fracture toughness on the material density. Finally, the mean value of such an index is compared with that obtained from the results (available in the literature) related to a previous experimental campaign performed on the same commercial PB.
  • Highly Effective E-heating Performance of Nickel Coated Carbon Fiber and
           its Composites for De-icing application
    • Abstract: Publication date: Available online 9 September 2019Source: Composite StructuresAuthor(s): Yanhong Cao, Farial Islam Farha, Dongsheng Ge, Xiaohua Liu, Wei Liu, Gen Li, Ting Zhang, Fujun Xu
  • Predicting damage initiation in 3D fibre-reinforced composites - the case
           for strain-based criteria
    • Abstract: Publication date: Available online 9 September 2019Source: Composite StructuresAuthor(s): Carolyn Oddy, Tomas Ekermann, Magnus Ekh, Martin Fagerström, Stefan Hallström, Fredrik Stig Three dimensional (3D) fibre-reinforced composites have shown weight efficient strength and stiffness characteristics as well as promising energy absorption capabilities. In the considered class of 3D-reinforcement, vertical and horizontal weft yarns interlace warp yarns. The through-thickness reinforcements suppress delamination and allow for stable and progressive damage growth in a quasi-ductile manner.With the ultimate goal of developing a homogenised computational model to predict how the material will deform and eventually fail under loading, this work proposes candidates for failure initiation criteria. It is shown that the extension of the LaRC05 stress-based failure criteria for unidirectional laminated composites, to this class of 3D-reinforced composite presents a number of challenges and leads to erroneous predictions. Analysing a mesoscale representative volume element does however indicate, that loading the 3D fibre-reinforced composite produces relatively uniform strain fields. The average strain fields of each material constituent are well predicted by an equivalent homogeneous material response. Strain based criteria inspired by LaRC05 are therefore proposed. The criteria are evaluated numerically for tensile, compressive and shear tests. Results show that their predictions for the simulated load cases are qualitatively more reasonable.
  • Influence of the degree of damage and confinement materials on the seismic
           behavior of RC beam-SRC column composite joints
    • Abstract: Publication date: Available online 7 September 2019Source: Composite StructuresAuthor(s): Sheng Peng, Chengxiang Xu, Chenfei Wang, Zuotao Ma The seismic behavior of reinforced concrete (RC) beam-steel-reinforced concrete (SRC) column composite joints strengthened with carbon fiber-reinforced polymer (CFRP) sheets and enveloped steel jackets (ESJ) was investigated. Based on the existing regulations, nine specimens were designed and built to simulate pre-damage loading, rehabilitation with CFRP sheets or ESJ, and destruction tests under lateral cyclic loading to determine the performance of the two reinforcement materials (CFRP sheets and ESJ) for different degrees of seismic damage. An analysis of the hysteretic curves, skeleton curves, ductility, energy dissipation, bearing capacity degradation, stiffness degradation, and strain-displacement curves of the specimens indicated that the two strengthening materials exhibited good reinforcement performance. The ESJ improved the bearing capacity and stiffness of the specimens and the CFRP sheets improved the ductility and energy dissipation of the specimens, thereby improving the seismic behavior of the specimens. The severely damaged specimen strengthened with the CFRP sheets or ESJ did not collapse in a simulated strong earthquake and was similar to or even exceeded the seismic performance of the original specimen; this result is important and applicable to engineering practice. The ductility and energy dissipation was lower for the ESJ-strengthened specimen than the CFRP-strengthened specimen. Therefore, the ESJ material is preferable when only one type of material is used for strengthening the specimen. The seismic performance of the RC beam-SRC column frame joints strengthened with the CFRP sheets and ESJ was simulated using the finite element analysis software ABAQUS. There was a good agreement between the simulation results and the experimental results. It was proved that the simulated and experimental results of the ultimate bearing capacity of the joints in the core zones were in good agreement, which meets the design principle of “strong joint, weak member”.
  • A critical review and assessment for FRP-concrete bond systems with epoxy
           resin exposed to chloride environments
    • Abstract: Publication date: Available online 6 September 2019Source: Composite StructuresAuthor(s): Jianglin Li, Jianhe Xie, Feng Liu, Zhongyu Lu Fiber-reinforced polymer (FRP) composites have been widely used for retrofitting concrete structures. Furthermore, increasing numbers of researchers are concerned about the use of FRP as an externally bonded reinforcement in coastal areas. The short-term performance of FRP-strengthened concrete structures has been intensively investigated; however, the long-term properties of FRP-concrete bond systems in chloride environments have been relatively less frequently investigated to date. For the safe and economic use of FRP as a promising structural material, the durability of concrete structures externally strengthened with FRP needs to be properly understood. This study presents the recent progress and achievements in the performance of FRP-concrete bond systems subjected to chloride exposure. The durability of epoxy resin, FRP composites and the FRP-concrete interface in immersion exposure and wet-dry cycle exposure is focused in this review. The mechanism of typical failure modes of FRP-concrete interface is further investigated. Moreover, the lower bound limit of the tensile property retention of epoxy resin and FRP composites is analyzed and compared with the published specifications. Finally, recommendations for future research are also presented.
  • Topology optimization of 2-D mechanical metamaterials using a parametric
           level set method combined with a meshfree algorithm
    • Abstract: Publication date: Available online 24 August 2019Source: Composite StructuresAuthor(s): L. Ai, X.-L. Gao Two-dimensional (2-D) micro-architectured mechanical metamaterials are designed using a topology optimization approach that integrates a parametric level set method (PLSM) with a meshfree method based on compactly supported radial basis functions (CS-RBF). The PLSM is employed as the optimization algorithm to achieve desired microstructures with targeted material properties. The effective elastic properties, including the bulk modulus, shear modulus and Poisson’s ratio, are predicted using a strain energy-based homogenization method and the CS-RBF meshfree algorithm. Two sets of optimizations are implemented: one is for the case of a single solid material, and the other is for the case of two solid materials, each involving an additional void phase. Three numerical examples are provided for each case with the same optimization objectives: maximizing the effective bulk modulus, maximizing the effective shear modulus, and minimizing the effective Poisson’s ratio under given volume fraction constraints. The numerical results reveal that the newly proposed approach can generate smooth topological boundaries and optimal microstructures. In particular, the current method can topologically optimize auxetic metamaterials with a negative Poisson’s ratio. It can also be extended to design other periodic metamaterials, including those with a negative coefficient of thermal expansion or frequency bandgaps.
  • Effect of surface micro-pits on mode-II fracture toughness of
           Ti-6Al-4V/PEEK interface
    • Abstract: Publication date: Available online 17 August 2019Source: Composite StructuresAuthor(s): Lei Pan, Xiaofei Pang, Fei Wang, Haiqiang Huang, Yu shi, Jie Tao Herein, the delamination issue of TiGr(TC4/PEEK/Cf) laminate is addressed by investigating the influence of TC4(Ti-6Al-4V) surface micro-pits on mode-II interfacial fracture toughness of TC4/PEEK interface through experimental and finite element modeling. The micro-pits unit cell, unit strip and the end notched flexure (ENF) models are established based on the finite element simulations and the effect of micro-pit size parameters is studied in detail. The results of micro-pits unit cell model reveal that the presence of micro-pits can effectively buffer the interfacial stress concentration under mode-II loading conditions. Furthermore, the micro-pits unit strip model, with different micro-pit sizes, is analyzed to obtain the interface parameters, which are converted and used in the ENF model. Both the unit strip and ENF models conclude that the presence of interfacial micro-pits effectively improves the mode-II fracture toughness. It is worth mentioning that the utilization of converted interface parameters in ENF model avoided the limitation of micro-pit size and reduced the workload. Finally, the experimental and computational ENF results exhibited excellent consistency and confirmed the reliability of the proposed finite element models. The current study provides useful guidelines for the design and manufacturing of high-performance TC4/PEEK interfaces for a wide range of applications.
  • Modeling the non-trivial behavior of anisotropic beams: a simple
           Timoshenko beam with enhanced stress recovery and constitutive relations
    • Abstract: Publication date: Available online 2 August 2019Source: Composite StructuresAuthor(s): Giuseppe Balduzzi, Simone Morganti, Josef Füssl, Mehdi Aminbaghai, Alessandro Reali, Ferdinando Auricchio In this work we analyze the non-trivial influence of material anisotropy on the structural behavior of a multi-layer planar beam. Indeed, analytical results available in literature are limited to homogeneous beams and several aspects have not been addressed yet, preventing a deep understanding of the mechanical response of anisotropic structural elements. This paper proposes an effective recovery of stress distributions and an energetically consistent evaluation of constitutive relations to be used within a planar Timoshenko beam model. The resulting structural analysis tool highlights the following peculiarities of anisotropic beams: (i) the transversal internal force affects the maximum axial stress up to 30%, and (ii) the anisotropy influences the beam displacements more than the standard shear deformation, even for extremely slender beams. A rigorous comparison with analytical and accurate 2D Finite Element solutions confirms the accuracy of the proposed approach, which leads to errors usually below 2%.
  • Experimental and mesoscopic investigation of double-layer aluminum foam
           under impact loading
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Jinhua Zhang, Li Chen, Hao Wu, Qin Fang, Yadong Zhang This paper focuses on the mechanical response of double-layer aluminum foam under static and impact loading. In the first part, experimental investigations are conducted to research the static and dynamic response of aluminum foam. The mechanical response of single- and double-layer specimens is discussed. In the second part, a mesoscopic model is developed based on X-ray CT (computed tomography) images. The mesoscopic characteristics of aluminum foam cells in size, shape, and distribution are considered according to the statistical results. Simulations reveal that the presented mesoscopic model can reliably predict the mechanics of aluminum foam. At last, it conducts study on the dynamic response of the aluminum foam employing the mesoscopic model. It discusses the mesoscopic deformation mechanism of double-layer specimens under high-velocity impact. Results show that the density arrangement is critical to the dynamic crushing.
  • Virtual testing of mechanical response of composite plates with normally
           distributed wrinkles
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): Chuanchuan Shen, Li Ma, Ping Xu, Jinyang Zheng In this paper, a new method combined three-dimensional finite element method (FEM) with heterogeneity model of wrinkles was presented to predict the mechanical response of orthotropic plates under four different loading conditions: transverse compression, axial tension, bending and shearing. The effective elastic properties disturbed by wrinkles are determined based on a mesomechanics model and a homogenization technique. The computation combining heterogeneous wrinkles can be considered as a virtual test since it allows every computation to produce a different result according to different shapes, sizes and locations of wrinkles, which are believed to obey the normal and random distribution, respectively. It was found that the in-plane displacements of plates increase dramatically when the heterogeneity wrinkle model is considered. The fluctuant displacement fields of the plate under axial tensile load can be clearly observed, and the distortion of displacement contours becomes serious with the increment of standard deviation of normally distributed wrinkle defects. Also, the statistical characteristics of mechanical response corresponding to different standard deviations were obtained according to multiple computations.
  • Bloch wave based method for dynamic homogenization and vibration analysis
           of lattice truss core sandwich structures
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): Jiajia Guo, Yong Xiao, Shufeng Zhang, Jihong Wen A unified semi-analytical method for dynamic homogenization and vibration analysis of lattice truss core sandwich beams is proposed. The method is developed based on prediction of both propagating and evanescent Bloch waves in the periodic truss core sandwich beam using a wave finite element method. This is accomplished very efficiently with the requirement of modeling only one unit cell of the periodic sandwich beam, which can be implemented simply by employing a conventional finite element package. A dynamic equivalent Timoshenko beam model is thereby built by matching its propagating and evanescent flexural wavenumbers to those predicted from the original sandwich beam. Dynamic equivalent beam parameters including equivalent flexural stiffness, equivalent shear stiffness, as well as equivalent Young’s modulus and shear modulus are identified and expressed as explicit formulations relating to the two matched flexural wavenumbers. Free vibrations of finite-length lattice truss core sandwich beams with various common boundary conditions are further examined based on analytical natural frequency equations and normal mode functions. It is demonstrated that the proposed method shows excellent agreement with conventional finite element method and provides much better accuracy of natural frequency prediction than a representative existing method.
  • Experimental Investigation of Frictional Behavior in a Filament Winding
           Process for Joining Fiber-Reinforced Profiles
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): Marius Dackweiler, Lorenz Hagemann, Sven Coutandin, Jürgen Fleischer Filament winding with a rotating ring allows the joining of hollow, fiber-reinforced profiles. To avoid fiber slippage and to be able to produce wound connections, the curvature of the winding path as well as the friction between mandrel and fibers must be considered. In this paper, the frictional behavior of dry carbon fiber tows is investigated in the context of filament winding for joining profiles. Friction experiments using a sled and filament-winding experiments are performed in order to examine the interrelationship between both setups. Furthermore, the influence of parameters, such as fiber orientation and contact surface, are analyzed. Regarding the frictional behavior of dry carbon fibers, it is found that the perpendicular slippage of the tow is governed by different mechanisms. Therefore, two different modes of slippage can be distinguished, depending on whether the tow’s limit of adhesion is dominated by the friction between the mandrel surface and the bottom layer of filaments, or by the coherence of filaments within the tow.
  • Non-linear vibration response of functionally graded circular cylindrical
           shells subjected to thermo-mechanical loading
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): Amit Yadav, Marco Amabili, Sarat Kumar Panda, Tanish Dey The analysis of the non-linear vibration response is carried out for functionally graded (FG) circular cylindrical shells subjected to thermal environment along with mechanical in-plane non-uniformly distributed loading along the edges and harmonic radial force. The temperature dependent material properties of the simply supported shell are assumed to vary in the radial direction according to power-law distribution. Based on the first-order shear deformation theory and von-Kármán type geometric nonlinearity, the strain-displacement relationships are established for circular cylindrical shells. The coupled governing equations of motion for functionally graded cylindrical shells are then derived using Hamilton’s principle. Employing Galerkin’s method, the coupled partial differential equations of motions are reduced to a set of non-linear ordinary differential equations. In order to obtain the free and forced vibration response of the FG shell, the incremental harmonic balance method, in conjunction with the arc-length method, is used. The non-uniform in-plane loading is converted to Fourier series and the pre-buckling analysis is performed to determine the stress distribution within the shell. The non-linear frequency-amplitude response is studied to examine the effects of volume fractions of the constituents, static partial edge loadings, thermal loads, and radial periodic loadings.
  • An overview of burst, buckling, durability and corrosion analysis of
           lightweight FRP composite pipes and their applicability
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): M. Manoj Prabhakar, N. Rajini, Nadir Ayrilmis, K. Mayandi, Suchart Siengchin, K. Senthilkumar, S. Karthikeyan, Sikiru O. Ismail The main aim of this review article was to address the performance of filament wound fibre reinforced polymer (FRP) composite pipes and their critical properties, such as burst, buckling, durability and corrosion. The importance of process parameters concerning merits and demerits of the manufacturing methods was discussed for the better-quality performance. Burst analysis revealed that the winding angle of ±55° was observed to be optimum with minimum failure mechanisms, such as matrix cracking, whitening, leakage and fracture. The reduction of buckling effect was reported in case of lower hoop stress value in the hoop to axial stress ratio against axial, compression and torsion. A significant improvement in energy absorption was observed in the hybrid composite pipes with the effect of thermal treatment. However, the varying winding angle in FRP pipe fabrication was reported as an influencing factor affecting all the aforementioned properties. Almost 90% of the reviewed studies was done using E-glass/epoxy materials for the composite pipe production. By overcoming associated limitations, such as replacing synthetic materials, designing new material combinations and cost-benefit analysis, the production cost of the lightweight FRP composite pipes can be decreased for the real-time applications.
  • Review of Through-the-thickness Reinforced Composites in Joints
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): N. Sarantinos, S. Tsantzalis, S. Ucsnik, V. Kostopoulos The present paper reviews the novel area of composite to composite and composite to metal joining, utilizing novel 3D reinforcement technology. The 3D reinforcement pinned technology extends the use of micro-pins from through-the-thickness laminate reinforcement to joints, while introducing AM (Additive Manufacture) and CMT (Cold Metal Transfer) technologies to the joint research field. The great advantages that this novel joining technique provides are lightweight connection, increased strength and significant improvement in damage tolerance. However, the concept has not been extensively explored in all loading nor environmental conditions and on the effects of the various design and manufacturing parameters.
  • Effect of fiber hybridization on mechanical performances and impact
           behaviors of basalt fiber/ UHMWPE fiber reinforced epoxy composites
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): Zhiming Yang, Jinxu Liu, Fuchi Wang, Shukui Li, Xinya Feng In order to investigate the effect of fiber hybridization on the mechanical performances and impact behaviors of basalt fiber (BF)/ UHMWPE fiber (PEF) reinforced epoxy composites, the BF/PEF hybrid composites were fabricated by the mould pressing method. For comparison, the BF composites and the PEF composites were also fabricated. The quasi-static tensile, quasi-static compression and dynamic compression properties of these composites were studied. Meanwhile, the low-velocity impact and high-speed impact properties were analyzed. Thanks to the good matching of strength and toughness, the 60BF/40PEF composites exhibit better critical failure energy absorption capability and low-velocity impact properties than that of the BF composites and the PEF composites. Moreover, during ballistic test, because the BF has a low thermal conductivity, the BF layers can inhibit the conduction of rising temperature to PEF layers in the process of high-velocity impact, and the advantages of high axial tensile strength of the PEF can be fully utilized, which is responsible for the best ballistic performance of the 60BF/40PEF composites.
  • Fabrication of bamboo-structure hollow polyester monofilaments for
           extraordinary compression properties
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): Xiaohui Zhang, Xin Wang, Yantao Gao, Pibo Ma Owing to its special structure, bamboo can withstand larger load in nature. The novel structure of bamboo is a great example for exploring materials with excellent mechanical properties, though limited research in this area has been reported so far. In textiles, monofilaments with outstanding compression property are desired in the development of warp-knitted spacer fabrics for a range of applications. Herein, we use 3D printing method to fabricate polyester (PET) bamboo-structure monofilaments and study their compression properties. It has been found that bamboo-structure hollow monofilament undertakes more load per unit mass than solid and continuous hollow monofilaments, and the value of load per unit mass increases with the increase of the hollow part. FEM analysis has discovered that the compression behavior and the compression properties of the bamboo-structure monofilament are in accordance with that of spacer monofilament in warp-knitted spacer fabrics. Warp-knitted spacer monofilaments prepared from bamboo-structure hollow monofilament with a high percentage of hollow part undertake more load per unit mass, providing new opportunities on the design and development of warp-knitted spacer monofilament towards different applications.
  • Characterizing Fracture Response of Cracked Transversely Graded Materials
    • Abstract: Publication date: Available online 14 September 2019Source: Composite StructuresAuthor(s): Behrad Koohbor, Milad Rohanifar, Addis Kidane Property gradation along a crack front makes conventional fracture mechanics analyses challenging. This issue is addressed in the present study through a combination of full-field measurements and modeling. We develop a novel experimental setup that consists of a synchronous dual Digital Image Correlation (DIC) system, facilitating in situ measurement of displacement and strain fields on both surfaces of a transversely precracked multi-layered structure subjected to uniaxial tensile load. By measuring the evolution of stress intensity factors developed on the opposite sides of the sample, we explore the mechanisms of crack initiation and propagation in the examined graded sample. Our experimental measurements are supplemented by a finite element analysis that elucidates the deformation and fracture response of the internal layers for which surface measurement is not possible. Finally, based on experimental and numerical observations, we develop a simple model that allows for prediction of critical far-field loads at which transversely graded structures fail. The capability of our proposed model in predicting tensile failure loads is demonstrated through a brief study of the influence of gradient function on the load bearing and fracture resistance in various graded structures.
  • 3D static analysis of patched composite laminates using a multidomain
           differential quadrature method
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): S.O. Ojo, P.M. Weaver Fibre Patch Placement (FPP) technology offers the opportunity to overcome the limitations of continuous fibre tape technologies by producing patched composite laminates with variable-stiffness properties that can achieve a load path optimized structural design. Current numerical models based on thin plate mechanics do not capture interlaminar stresses and so fail to predict failure of patched laminates as instigated by such 3D stress fields. This study investigates 3D static performance of patched laminates using Unified Formulation (UF) for beams based on strong- and weak-forms, multidomain differential quadrature method (MDQM) and high-order finite element method (HOFEM) respectively. The study shows that under static loadings, the structural performance of patched laminates is locally influenced by the presence of discontinuities and the intensity of the local effect depends on the laminate sequence as well as the type of loading. Also, the global behaviour of patched laminates under static loadings is not significantly impaired by discontinuities, which supports experimental findings in the literature. Finally, the results of the proposed models prove computationally efficient with about 97% fewer degrees of freedom for MDQM and HOFEM models compared to ABAQUS models of similar accuracy.
  • Using DIC technique to characterize the Mode II interface fracture of
           layered system composed of multiple materials
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): Jiangtao Yu, Yichao Wang, Zhanhong Li, Qian Zhang, Xiangru Jian, Zhigang Zhang This article introduces a new method developed for characterizing the mode-II dominant interfacial fracture in a layered system composed of materials with significantly different mechanical properties. The proposed method consists of 3 parts. First, using digital image correlation (DIC) technique to acquire the full field strain in layered composites and then calculating the variation of elastic strain energy in multiple loading steps. Second, using DIC to acquire the relative displacement between layers and then calculating the possible strain energy release rates in multiple loading steps based on a presumptive bi-linear cohesive zone model (CZM) with unknown parameters. Third, developing an algorithm to find the optimal solutions for the presumptive bi-linear CZM by equilibrating the elastic strain energy and fracture energy with the minimum error in multiple loading steps. For verification, the proposed method was applied to characterize the mode II dominated interface fracture of a bi-material and bi-layer system under tension. The feasibility and accuracy of the proposed method are experimentally demonstrated.
  • Development of two intrinsic cohesive zone models for progressive
           interfacial cracking of laminated composites with matching and
           non-matching cohesive elements
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): Shunhua Chen, Naoto Mitsume, Tinh Quoc Bui, Wei Gao, Tomonori Yamada, Mengyan Zang, Shinobu Yoshimura In recent decades, intrinsic cohesive zone models (CZMs) have proved to be an effective approach to modeling progressive interfacial cracking of laminated composite structures. However, matching cohesive interface elements are usually required, which imposes constraints on finite element mesh discretization and reduces computational efficiency for interfacial cracking analysis in bi-material structures with a large modulus mismatch. To address this issue, we develop two intrinsic CZMs, i.e. node- and facet-based models, allowing interfacial cracking modeling with both matching and non-matching cohesive elements in a unified way. Prior to cracking simulations, node and facet cohesive pairs can be easily constructed by recourse to contact detection algorithms. During cracking, cohesive forces of such two models are evaluated in pointwise and integral ways, respectively. The developed models are then respectively coupled with tributary node-to-segment and mortar algorithms to account for a smooth transition from cohesive failure to unilateral contact. Several representative numerical examples are performed to validate the effectiveness of the proposed models, where the numerical performance is also compared and discussed.
  • An investigation on fatigue life evaluation and crack initiation of
           Al-GFRP bonded lap joints under four-point bending
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): Pedram Zamani, Abdolrahman Jaamialahmadi, Lucas F.M. da Silva, Khalil Farhangdoost In this paper, fatigue life and crack initiation of aluminum-GFRP bonded lap joints are investigated under four-point bending loading. For this purpose, a new fixture was designed and constructed. Fatigue loads vs. number of cycles to failure (L-N) were obtained so that the influence of various load ratios on L-N were examined. Furthuremore, the load amplitude vs. number of cycle curves were investigated. In addition, the load amplitude vs. mean load curve was obtained at 100000 cycles. The effect of different maximum fatigue loads and load ratios were investigated on crack initiation life by implementing the backface strain (BFS) measurement and using an optical microscope. From the results, it can be inferred that the life of the crack initiation phase is nearly equal to that of half of the total life for a maximum load of 50% of the static failure load, whereas it is negligible for maximum fatigue loads higher than 60% of the static failure load. It was found that for a load ratio of R=-1, the crack initiation phase is negligible. Moreover, It was found that BFS plots were ended to the L-N curve, and this curve could be considered as a limit for BFS plots. Finally, a combined diagram including L-N curve, BFS, initiation, and rapid failure curves can be used to predict the remaining life of a joint which is loaded up to a certain number of cycles.
  • Evaluation of complex spectrum of the symmetrical Lamb waves for
           three-layered plates at low frequency. Part II: Asymptotics/numerical
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): D.D. Zakharov, A.V. Nikonov Developing the approach outlined in Part I, the wavenumber spectrum is evaluated. Firstly, for the nth complex dispersion curve the asymptotics of the wavenumber’s static value is considered as n→+∞. Two approaches to obtain this asymptotics are compared. Then, for any n the exact value in statics is calculated using iterations, starting with the asymptotic value as the initial approximation. The parametric analysis revealed a specific (critical) value of the geometrical parameter at which the wavenumbers are redistributed. Secondly, the low frequency asymptotics of the dispersion curves are obtained. They exibit the flat initial segment of each complex dispersion curve which is the longer, the larger is the index n of the curve. Thus, this part of spectrum can be described by simple analytical formulas. The exact dispersion curves are evaluated using another iterative algorithm for improving the approximations. For both steps the numerical results are in a good agreement with the asymptotics. Finally, the perspectives of the method for other composite structural members are discussed.
  • Magnetic Actuation Bionic Robotic Gripper with Bistable Morphing Structure
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): Zheng Zhang, Xianghao Li, Xiaochen Yu, Hao Chai, Yang Li, Huaping Wu, Shaofei Jiang Soft robotics is an emerging research field that uses deformable materials or structures to fabricate compliant and adaptable systems through simple integrated mechanisms, thereby, enabling biomimetic behaviour. The Venus flytrap has the characteristics of excellent responsiveness and deformability, making it a promising inspirational model for the development of soft robotics. This paper presents a novel robotic gripper that mimics the trapping motion of the Venus flytrap. This gripper was implemented by exploiting a combination of bistable anti-symmetric shells and magnetic actuation. Two cylindrical shells constructed from carbon-fibre-reinforced polymer act as compliant fingers that can transform between two stable configurations based on external actuation. An applied clamped boundary condition reduces the actuation force required to trigger the morphing process. A novel non-contact magnetic actuation method with excellent responsiveness is proposed to actuate the compliant finger. The robotic gripper is designed to be lightweight and compact with high gripping force. Experiments and simulations were performed to analyse the gripping motion and measure the actuation force. The width of the clamped edge is the main factor influencing gripper performance as it relates to actuation force. The results of our analysis demonstrate that the proposed flytrap-inspired design with a bistable structure can be used to implement a novel robotic gripper controlled by a magnetic field.
  • Toughening Efficiency and Mechanism of Carbon Fibre epoxy matrix
           composites by PEK-C
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): Jiawei Yao, Kangmin Niu, Yifan Niu, Teng Zhang Polyaryletherketone with Cardo (PEK-C) was used as matrix additive, film and particle interleaves to improve the fracture toughness of carbon fibre epoxy matrix composites. The toughening efficiency and mechanism of the three methods were studied. The PEK-C film interlayer was more efficient and stable in the interlanimar toughening. The flexural strength was not compromised with the incorporation of PEK-C due to the limited addition. The enhanced interlaminar toughening was mainly attributed to the two-phase structure of micrometer scale formed by PEK-C “peel” and the rounded epoxy matrix wrapped by PEK-C. The nanoscale sea-island substructure in the rounded epoxy matrix was observed by atomic force microscopy (AFM), which might be also correlated with the toughness improvement.
  • Evaluation of complex spectrum of the symmetrical Lamb waves for
           three-layered plates at low frequency. Part I: Foundations
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): D.D. Zakharov, A.V. Nikonov A new method combining the asymptotic and iteration approaches to study the total wavenumber spectrum for a plate made of isotropic layers is suggested. In this part we use the propagator matrices to deduce the dispersion equation and its static limit in a closed form with the use of symbolic calculations. The roots in statics which are analyzed at the first step play the key role. Then, the low frequency approximations for the dispersion curves are derived. The method is aimed to evaluate a dispersion curve of any order n and to describe it in a closed form by an asymptotic formula. Especially it concerns the case n→+∞ which causes difficulty for the pure numerical approaches.
  • Dimension reduction and surrogate based topology optimization of periodic
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): Min Li, Zhibao Cheng, Gaofeng Jia, Zhifei Shi The frequency bandgap of periodic structures has many potential applications. Topology optimization of the unit cell of periodic structures offers great potential to design periodic structures with desirable bandgap characteristics. However, topology optimization typically involves many design variables stemming from discretization of the unit cell. This creates computational challenges for both optimization (i.e., high-dimensional discrete design variables) and the calculation of frequency bandgaps for a given design (i.e., finer discretization requires higher computational effort). To address these challenges, this paper proposes an efficient dimension reduction and surrogate based approach for topology optimization of periodic structures. Using information from a set of reference topologies with more desirable bandgap characteristics, dimension reduction technique (i.e., logistic principal component analysis) is used to establish a low-dimensional representation of different topologies in latent design space. To reduce computational effort in calculation of bandgap, Kriging surrogate model is built with respect to the low-dimensional latent continuous design variables, and used within efficient global optimization to efficiently and adaptively identify the optimal topology. The effectiveness and great efficiency of the proposed approach are verified through an example on topology optimization of 2D periodic structures to maximize the in-plane frequency bandgaps.
  • A microwave absorption/transmission integrated sandwich structure based on
           composite corrugation channel: design, fabrication and experiment
    • Abstract: Publication date: Available online 13 September 2019Source: Composite StructuresAuthor(s): Wei Jiang, Hua Ma, Leilei Yan, Jiafu Wang, Yajuan Han, Lin Zheng, Shaobo Qu A microwave absorption/transmission integrated sandwich structure (MATSS) with excellent mechanical properties was proposed and investigated in this paper. This structure is composed of composite corrugation panels with foams filled in its channels. The absorption/transmission property is produced based on the mechanism of spatial dispersion engineering and electromagnetic resonance. Different from previous designs, this proposal can realize a broadband absorption (5.74-7.84 GHz) below transmission band (8.96-12.45 GHz) with the absorptivity and transmissibility more than 80%. Moreover, compressive experiment results show that filling foams in channels can obviously improve the mechanical properties of this structure. The peak compressive strength of the foam-filled MATSS can reach to 25.21 MPa with a core density 0.32 g/cm3, which are more competitive comparing with many metallic sandwich core topologies.
  • Nonlinear random responses and fatigue prediction of elastically
           restrained laminated composite panels in thermo-acoustic environments
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Yilong Wang, Dengqing Cao, Jiaqi Peng, Hao Cheng, Huagang Lin, Wenhu Huang This paper presents a formulation for predicting the nonlinear random response of the elastically restrained laminated composite panel subjected to thermo-acoustic loads. Based on the laminated plate theory and Von Kármán large deflection and classical thin plate theories, the natural characteristics are obtained via Rayleigh-Ritz method and then the governing equations of the panel subjected to combined acoustic and thermal loads are formulated. The nonlinear partial differential equations of motion are transformed to a set of coupled nonlinear ordinary differential equations in truncated modal coordinates. A numerical example where the acoustic load is considered as the Gaussian band-limited white noise is given to perform the process of obtaining the mode and responses of the panel. Taking the natural frequency obtained from the finite element method as a reference value, the process of obtaining the natural frequencies is validated by comparing the frequency results. Numerical results show that the buckling, snap-through, and nonlinear random vibrations of the thermal-elastic restrained panel can be predicted accurately. Comparing stress PSD distributions with fatigue damage distributions, the first-order mode is proved to be valid for determining the most dangerous area for fatigue life prediction.
  • Bending model for a laminated composite cantilever beam with multiple
           embedded shape memory alloy layers presenting tensile-compressive
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): N.V. Viet, W. Zaki A new model is proposed for a composite laminated beam comprising multiple alternating shape memory alloy (SMA) and elastic layers. The model fully considers asymmetry in SMA behavior, which is found to significantly influence the behavior of the laminates. Moreover, the equations governing the response of the SMA-reinforced beams are derived for a complete loading-unloading cycle considering a Timoshenko beam deformation model combined with well-established constitutive relations for SMAs. The derivation procedure involves first identifying the solid phase structure of the beam for a given applied load, followed by integration of the stress and strain in a cross section to obtain moment and shear force equations. The influence of temperature, as well as of layer thickness and material properties on the bending response of the beam is investigated. The results obtained using the proposed model are found to agree with finite element simulations.
  • Fiber bridging in composite laminates: a literature Review
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Rafiullah Khan Fiber reinforced composites are quickly replacing their metal counterparts in the structural applications due to their higher specific strength and stiffness. The fiber bridging increases the fracture toughness of the composites several times. At the same time, the characterization of the composites is challenging due to fiber bridging. Large number of studies has been devoted to investigate various aspects of fiber bridging phenomenon in the composites. This paper is a comprehensive review of the literature studies on fiber bridging. The paper is mainly focused on the origin of fiber bridging, bridging laws, experimental investigations and cohesive zone modeling of the delamination in the presence of fiber bridging. The fatigue delamination growth characterization in the presence of fiber bridging and the significance of stitching/z-pinning are also briefly discussed in this literature review.
  • A mean-field homogenisation scheme with CZM-based interfaces describing
           progressive inclusions debonding
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Timothée Gentieu, Anita Catapano, Julien Jumel, James Broughton The objective of the present study is to describe the progressive debonding of inclusions in particle or fibre reinforced composites. To do so, the mean-field homogenisation scheme of Mori-Tanaka is enriched to take into account imperfect interfaces. The interfaces are modelled by a bilinear Cohesive Zone Model (CZM) taking into account normal and tangential effects. Results obtained with this new mean-field homogenisation scheme are compared to 2D FE-based numerical simulations that are used as reference results. The effects of inclusions volume fraction and size are also observed.
  • Analysis of Vibration Reduction Characteristics of Composite Fiber Curved
           Laminated Panels
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Wang Xianfeng, Wang Huaqiao, Ma cheng, Xiao Jun, Li Liang Firstly, based on modal experiment, this paper analyses composite fiber curve laminates, which includes []8, []8, []8, []8, []8, []8, and then gets damping ratio of each laminated plate. After analysis, the results showed that the curve of fiber layer for composite laminated plate damping ratio is the maximum, however, the curve of fiber layer for composite laminated plate damping ratio is the maximum. Secondly, the simple harmonic test of laminated plates with curved layers was carried out. Those plates includes [0/45//-45]s, [0/45//-45]s, [0/45//-45]s, [0/45//-45]s, [0/45//-45]s, [0/45//-45]s. It is easy to get the acceleration response maps of each laminated plate. The above simple harmonic test results showed that larger the damping ratio, the better the damping effect and the smaller the amplitude of acceleration. The amplitude of acceleration changes inversely with the change of damping ratio. Finally, the conclusion is that the laminated plate with the best vibration damping effect is []8, and the laminated plate with the worst vibration damping effect is []8.
  • On the geometrically nonlinear analysis of sandwich shells with
           viscoelastic core: A layerwise dynamic finite element formulation
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): S.A. Hosseini Kordkheili, R. Khorasani The objective of this work is to present a finite element formulation for dynamic analysis of sandwich shells with viscoelastic core under large deformation. The present study is based on an incremental updated Lagrangian approach together with the Newmark integration scheme. The viscoelastic constitutive model which is used to define the behavior of the core, comes from the Riesz theorem and the corresponding creep functions are estimated using Dirichlet-Prony series. Also, the viscoelastic deferred strain is derived in an appropriate incremental form using the state variables. The employed layerwise shell element which is based on zig-zag theory has eight nodes on its mid layer. What’s more, in addition to three translational and two rotational degrees of freedom per node, the upper and lower layers are allowed to rotate independently relative to their neighbor layers. Thus, the damping effect of the viscoelastic core could be well described within the shear deformable displacement field. The presented nonlinear formulation is then implemented to a nonlinear finite element program to be appraised by solving different kinds of problems. The obtained numerical results correlate well with those available in the literature.
  • Fatigue behavior of concrete beams reinforced with glass- and carbon-fiber
           reinforced polymer (GFRP/CFRP) bars after exposure to elevated
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Jun Zhao, Guanghui Li, Zike Wang, Xiao-Ling Zhao This paper deals with fatigue performance of concrete beams with fiber reinforced polymer (FRP) bars after exposure to elevated temperatures. A total of 13 concrete beams reinforced with glass- and carbon-fiber reinforced polymer (GFRP/CFRP) bars were tested under static and fatigue loading after exposure to different levels of elevated temperatures. The influences of elevated temperature, holding time, fatigue load level and FRP bar type on the fatigue behavior of beams were investigated. The results showed that the elevated temperature exposure reduced more severely the fatigue life of GFRP-reinforced concrete beam than that of CFRP-reinforced beam below 400 oC, and GFRP- and CFRP-reinforced beams both lost their bearing capacities when the exposure temperature reached 600 oC. The elevated temperature accelerated the development of concrete strain, crack width and deflection of FRP-reinforced concrete beams with the number of fatigue cycles. The mid-span deflection was predicted using some existing models, and the CEB-FIP model showed the best accuracy with the coefficient of variation of 2.8-7.0%. The fatigue strength of GFRP- or CFRP-reinforced concrete beams is not affected by elevated temperatures up to 400 oC for 2 h.
  • Nonlinear Hermitian generalized hygrothermoelastic stress and wave
           propagation analyses of thick FGM spheres exhibiting temperature,
           moisture, and strain-rate material dependencies
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): M. Shariyat, S. Jahanshahi, H. Rahimi The present article is dedicated to the dynamic stress and displacement distributions and hygrothermoelastic wave propagation and reflection responses of FG hollow spheres subjected to thermomechanical shocks. The strain-rate and temperature dependencies of the material properties are accounted for. Hence, the material properties of the sphere are dependent on coordinates, time, loading rate, temperature, and ambient humidity. Furthermore, material degradation due to moisture absorption is considered. It is the first time that such a complex and more realistic combination is taken into account in the wave propagation analysis. The nonlinear coupled Lord-Shulman-type generalized hygrothermoelasticity equations that are developed by the inclusion of the moisture absorption state variable into the free energy function, are solved by using a Galerkin-type finite element method, iterative solution algorithm, and a second-order Runge-Kutta time integration procedure. Results are extracted by using the C1-continuous Hermitian rather than common C0-continuous Lagrangian elements to guarantee exact continuity of the stresses at the mutual boundaries of the elements and preclude the numerical locking phenomenon. Comprehensive sensitivity analyses including the effects of various factors are performed. Results reveal the significant effect of the temperature, strain-rate, and moisture absorption on both the material properties and constitutive law and consequently, on the transient stress distribution and the hygrothermoelastic wave propagation/reflection phenomenon. Furthermore, the results confirm that in the FG structures, the thermal and stress wavefronts travel with variable and time-dependent speeds.
  • Novel criteria for strength predictions of open-hole composite laminates
           for preliminary design
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Cassio Wallner, Sergio Frascino Muller Almeida, Christos Kassapoglou In this work a novel modification of the well-known Whitney-Nuismer criteria is proposed with the aim of having a simple and yet accurate fracture criterion for the important problem of estimating the strength of composite laminates with circular open-holes. The novelty is the use of a critical path curve that makes the proposed criteria quite general and provides very good correlation with experimental data for a wide range of laminates and hole sizes even when the characteristic lengths are assumed as material constants. This assumption dramatically reduces the amount of required experimental testing making these criteria very suitable for preliminary design.
  • Numerical simulation of arbitrary holes in orthotropic media by an
           efficient computational method based on adaptive XIGA
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Xin Chen, Jiming Gu, Tiantang Yu, Ling Qiu, Tinh Quoc Bui We present in this paper an efficient computational approach based on an adaptive extended isogeometric analysis (XIGA) for simulation of arbitrary holes in orthotropic materials. The interfaces of holes are described by multiple level set functions so that the developed XIGA can capture the hole geometry without considering its interfaces. The approach is further enhanced by using the locally refined (LR) B-spline basis functions, which dominate over B-spline or non-uniform rational B-spline functions (NURBS) due to the local refinement. This study only deals with the structured mesh strategy for local refinement. The implementation of the local refinement is guided by posteriori error estimator based on stress recovery. Accuracy study is performed for isotropic media due to the availability of analytical solutions. For numerical experiments, different types of holes in orthotropic media are studied, and the computed numerical results are compared with reference solutions derived from ABAQUS (FEM). We also compare the convergence rate obtained by our adaptive local refinement with that derived from uniform global refinement to indicate the greater advantage of the developed adaptive XIGA.
  • Enhanced comprehensive performance of bonding interface between CFRP and
           steel by a novel film adhesive
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Lu Ke, Chuanxi Li, Nanhai Luo, Jun He, Yang Jiao, Yongming Liu A novel film adhesive was proposed to bond carbon fiber reinforced polymer (CFRP) laminas to steel substrates, and experimental validations for improved comprehensive bond performances are presented. This film adhesive was shown to possess excellent high-temperature resistance via dynamic mechanical analysis (DMA). A series of CFRP/steel double-lap joints (DLJs) with different bond lengths were experimentally studied, focusing on the failure modes, effective bond length, bond-slip relationship, and bond strength. The results show that the film-adhesive bonded joints fail in the mode of CFRP delamination, which indicates a stronger interfacial bond between the adhesive layer and adherends than the intra-laminar strength of CFRPs. The bonding interface has an effective bond length of approximately 65 mm, beyond which no increase of ultimate load can be achieved with the increase of bond length. The bond-slip relationship of the film-adhesive bonding interface exhibits a trapezoidal (ductile) shape, which is significantly different from the triangular (brittle) shapes for most paste-adhesive interfaces. Superior strength, ductility, and high-temperature resistance of the bonding interfaces in CFRP/steel composites are achieved due to the use of this film adhesive. The proposed study offers an alternative solution to an enhanced comprehensive property of the bonding interface in CFRP/steel composites.
  • Mechanical properties of Ti/CF/PMR polyimide fiber metal laminates with
           various layup configurations
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Yubing Hu, Yanan Zhang, Xuelong Fu, Gazi Hao, Wei Jiang The mechanical properties of Ti/CF/PMR polyimide fiber metal laminates (FMLs) with various layup configurations and fiber layer orientations (0°, 90°, and ±45°) were systematically investigated. The results suggest that the elastic modulus and tensile strength of the FMLs were determined by the interfacial adhesion, volume fraction, and layup direction of the carbon fibers. A model has been proposed herein to predict the corresponding relative tensile strengths. The FML specimens were subjected to the compressive stress on the upper surface and tensile stress on the lower surface under the function of flexural strength, while the delamination and local buckling failure occupied the main position. Interlaminar shear strength (ILSS) of the FMLs with surface-coated pretreatment was higher than that of the untreated specimens. The applied load was effectively transferred to the carbon fibers via polyimide resin. Then, the axial load was transferred to the adjacent fibers having the same orientation. The ILSS of unidirectional layered FMLs had the highest value, while that of FMLs with carbon fibers laminated at ±45° was relatively low. The interlaminar shear fracture tended to occur inside the layers oriented in the direction of maximum load or in the vicinity of such layers.
  • Structural Integrity Assessment on Cracked Composites Interaction with
           Aeroelastic Constraint by Means of XFEM
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Nur Azam Abdullah, Mahesa Akbar, Nanda Wirawan, Jose Luis Curiel-Sosa In this paper, a novel approach in assessing the structural integrity of cracked composite plates under the aeroelastic condition by using XFEM is presented. To the authors’ knowledge, this is the first time that aeroelastic condition is coupled in XFEM to model the crack propagations. Previous researches from the literature had only considered a static crack condition. This research focuses on determining the first failure experienced by the cracked composite plate, either the crack will propagate causing a fracture, or the composite plate will fail due to aeroelastic instability imposed at the critical flutter speed. The proposed scheme is used to solve the limitation in XFEM within Abaqus that only general static and implicit dynamic analysis can be performed. The structure is assumed to interact with minimal gust, and the deflections by time are expressed in the equation of periodic motion based on Fourier Series Function (FSF). The results show that at a particular fibre orientation, once the damaged composite plate is deformed due to the dynamics load at dive speed, it fails due to the crack propagation first instead of the flutter. In contrast, another fibre configuration shows good resistance to crack propagation and fails due to flutter instability.
  • Nonlinear Transient Dynamic Analysis of Laminated Composite Parabolic
           Panels of Revolution with Variable Thickness Resting on Elastic Foundation
    • Abstract: Publication date: Available online 12 September 2019Source: Composite StructuresAuthor(s): Özgür Kalbaran, Hasan Kurtaran In this article, nonlinear transient behavior of laminated composite Parabolic Panels of Revolution Structure(s) (PPRS) with variable thickness resting on elastic foundation is investigated using Generalized Differential Quadrature (GDQ) method. Winkler-Pasternak model is used to represent elastic foundation. Linear, arch, sine and cosine thickness functions are used to express variable thickness. In transient analyses, First Order Shear Deformation Theory (FSDT) is used to consider the transverse shear effects. Nonlineartiy is taken into account using Green-Lagrange nonlinear strain-displacement relations considering deepness effect. Virtual work principle is used to derive the equations of motion. Partial derivatives in the equation of motion are expressed with GDQ method and time integration is carried out using Newmark average acceleration method. Several problems are solved and compared with finite element results in order to validate the proposed method. After validation, effects of thickness functions, thickness variation parameter, geometric characteristic parameter of PPRS, boundary conditions, elastic foundation parameters as well as composite lamination scheme on nonlinear transient dynamic behaviour of PPRS are investigated.
  • A virtual experimental approach to evaluate transverse damage behavior of
           a unidirectional composite considering noncircular fiber cross-sections
    • Abstract: Publication date: Available online 5 September 2019Source: Composite StructuresAuthor(s): Gyu Jeong, Jae Hyuk Lim, Chunghyeon Choi, Sun-Won Kim This study investigated the transverse damage behavior of a unidirectional composite containing a complex microstructure having noncircular fiber cross-sections. For this purpose, a finite-element (FE) model based real microscopic images of the M55J/M18 composite was generated with the signed distance function (SDF) by the level-set method and the trimming mesh technique. In addition, the interphase zone was constructed along the interface between the fiber and the matrix. Subsequently, a virtual experiment simulating a three-point bending test was conducted with the generated FE model. Crack propagation analysis was carried out with the cohesive zone model (CZM) by applying transverse tension under plane strain condition. The crack length and propagation directions were compared to those of the three-point bending test. To make a nice correlation between the virtual experiment and actual experiment, the effects of the fiber shape, thermal residual stress, and various fracture toughnesses were investigated on the length and propagation direction of the cracks. It was found that, the fiber shape is vital to the inter-fiber distance and fiber volume fraction (Vf), which strengthen or weaken the stress concentration, thus making the propagation direction of the cracks warped and the length of cracks varied.Graphical abstractGraphical abstract for this article
  • Effects of crumb rubber aggregate on the static and fatigue performance of
           reinforced concrete slabs
    • Abstract: Publication date: Available online 5 September 2019Source: Composite StructuresAuthor(s): Jianhe Xie, Yuwen Zheng, Yongchang Guo, Rongxuan Ou, Zhihong Xie, Liang Huang The utilization of crumb rubber concrete (CRC) is a sustainable solution for dealing with waste tyres. The aim of this work is to investigate the effects of rubber instead of fine aggregates on the static and fatigue performance of reinforced concrete slabs. Based on a series of experiments conducted to determine the material properties of rubberized concrete, a total of eight one-way reinforced concrete slabs were cast, including six CRC slabs and two normal slabs as control specimens according to rubber content and load type, and then were tested under four-point bending loads. The deflection, concrete strain, steel strain and load-bearing capacity of the reinforced CRC slab with different rubber content under monotonic loading were firstly investigated. And then, the effect of rubber incorporation on the failure behavior of reinforced concrete slab was examined, including the fatigue damage evolution, failure mode and fatigue life. The results indicate that rubberized concrete with appropriate mix proportions has the potential to be used in structural members. However, a high rubber content may result in the over-reinforcement of the RC slab, and could be also detrimental to its fatigue life. High fatigue stress can degrade the bonding between the rubber and paste, suggesting that the advantages of rubber that facilitate energy absorption cannot be utilized. For the safe design of rubber as a replacement for fine aggregates, the content of rubber in RC slab is suggested to be no more than 10%.
  • Multiscale Optimal Design and Fabrication of Laminated Composites
    • Abstract: Publication date: Available online 5 September 2019Source: Composite StructuresAuthor(s): Narasimha Boddeti, David W. Rosen, Kurt Maute, Martin L. Dunn We present a general framework that digitally integrates the workflow for optimal design and fabrication of novel multiscale laminated fiber-based composites with spatially varying microstructure in each lamina of a flat or curved laminate. Given a design problem, our framework consists of three key components: 1) Design automation, 2) Material compilation, and 3) Digital fabrication. Design automation involves efficient simultaneous synthesis of optimal macroscale topology and spatially varying fibrous microstructure in a laminated composite, whereas digital fabrication comprises manufacture of the optimal structure. Material compilation is an intermediate process that translates the multiscale results of the design automation step to a digitally manufacturable arrangement of matrix and fibers within each layer of a laminate. These components constitute a digital thread and can be initialized by any method or process of choice. In this paper, we develop a multiscale topology optimization approach for design automation, new computational geometry algorithms for material compilation, and voxel-based material jetting for digital fabrication. We demonstrate and experimentally validate the extensive capabilities of our framework with various plate and shell structures that have potential applications in architecture, aerospace and soft robotics.
  • Preparation and Characterization of B4C Particle Coated
           Composites for Stab-Resistance
    • Abstract: Publication date: Available online 5 September 2019Source: Composite StructuresAuthor(s): Minmin Xia, Zhenzhen Quan, Xueli Wang, Jianyong Yu To improve the stab resistance but decrease the weight of the stab-resistant clothing, coated stab-resistant composites have been prepared by coating aramid fabric with boron carbide (B4C)/epoxy resin. At first, B4C dispersion was prepared and a three-factor, four-level orthogonal experiment was designed to determine the optimal dispersion combination. It was shown that when the particle diameter is 2.5 μm, mass fraction is 49% and stirring temperature is 30 °C, the particle dispersion is the most uniform, with the highest relative sedimentation height. Then, the B4C dispersion was mixed with the expoxy resin and coated onto the aramid fabric, after which, stiffness, pulling-out, tearing and quasi-static puncture tests were conducted on the coated fabric. The results showed that the stab resistance increases with the decrease in particle diameter as well as the increase in particle mass fraction. For coated composites, the ultimate puncture load per weight reached 486 N/g, 428% higher than that of uncoated samples. The anti-stinging mechanism of the coated composites has also been investigated by analyzing the surface and fracture morphologies and the load-displacement curves.
  • Micro drilling of carbon fiber reinforced polymer
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): Igor Basso, Marcelo Ferreira Batista, Renato Goulart Jasinevicius, Juan Carlos Campos Rubio, Alessandro Roger Rodrigues In this paper, an assessment of micro holes quality in carbon fiber reinforced polymer (CFRP) composite was based on thrust force and damage formation. Carbon fiber T300 reinforced polyphenylene sulfide (PPS) was micro drilled with 0.6 mm diameter twist drill under three different strategies: direct, supported and pilot drilling. It was observed that when thrust force was measured under uncut chip thickness smaller than 77.5% of the drill lips edge radius (re,lips) a size effect was detected. However, when this cutting condition is achieved, a drift was identified in the cutting force value showing a conversely behavior from that observed during micro cutting of metals. This effect was attributed to a rheological phenomenon taking place at reduced cutting condition. It was observed that smaller drill feeds per rotation play an important role upon the size effect and damages formation. Based upon the results, delamination damages were not found due to the low thrust force levels and small drill feeds per rotation acquired. It is proposed that different cutting strategies may be applied to mitigate the formation of defects at the entry and exit of the holes in micro drilling of composites.
  • SRVE modeling of particulate polymer matrix composites with irregularly
           shaped inclusions: Application to a green stone composite
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): D. Karimi, A.S. Milani Particulate polymer matrix composites (PPMCs) play a significant role in a wide range of applications from tissue engineering to aero-structures. Modeling thermoelastic properties of PPMCs can save sizable experimental time and costs, as it provides the capability of predicting the composite’s response to different loading conditions with acceptable accuracies. Micromechanical modeling approach is employed in this investigation to predict the thermoelastic properties of a new particulate polymer matrix composite, made of granite powder as inclusion and the acrylonitrile butadiene styrene (ABS) as matrix—called green stone composite. The reinforcing particles are modeled according to their shape irregularities. Namely, a statistical representative volume element (SRVE) is developed using the concept of integral range, with randomly distributed particles with irregular shapes. Experiments have been conducted to examine the validity of the proposed modeling approach. Numerical and experimental results both show that adding granite powder to pure ABS up to 38% (volume fraction) can notably increase the composite’s thermoelastic properties (bulk and shear moduli as well as thermal conductivity), as high as 200%.
  • Asymptotic expansion differential quadrature method for the analysis of
           laminated hemispherical shells
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): Ponkrshnan Thiagarajan, K.V. Nagendra Gopal An asymptotic shell theory is proposed for the analysis of hemispherical shells. Vibration characteristics of laminated specially orthotropic hemispherical shells are investigated using multiple scales asymptotic expansion method. The governing equations are formulated from the three dimensional elasticity equations without any initial assumptions. These equations are solved using differential quadrature method to obtain the numerical solution of the problem. Numerical results are presented for laminated hemispherical shells with an axial cut at the top for clamped-clamped boundary condition. A parametric study is conducted for different thickness ratios, angle of the axial cut, orthotropic ratios and laminate configurations.
  • New approach of pipelines joining using fiber reinforced plastics
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): M.H. Farag, E. Mahdi This study aims to introduce a new pipeline joining technique using fiber-reinforced (FRP) composites. To this end, a comprehensive experimental program has been carried out to evaluate the new technique. The experimental program consists of four phases. In phase 1, a fabrication process in which aluminum pipes were employed for both types of joining (i.e., welding and joining by FRP is presented and discussed. Two types of welding have been used to study their effect on the pipe’s mechanical behavior. These are V welding and standard faced butt-welding techniques. For FRP joining, there are three types of fibers used. These are Kevlar fiber/epoxy (KFRP), carbon fiber/epoxy (CFRP), and glass fibers/epoxy (GFRP). Effect of fiber orientation angles of the joining system under three-point bending has been taken place in phase 2. The results showed that 00/900 orientation recorded the highest flexural load. In phase 3, the evaluation of welding types and fiber types effects on the bending behavior of joined pipes have been carried out. For the impact of welding types, V-welded pipes showed higher mechanical performance than normal faced butt-welded pipes. In addition, CFRP and KFRP joining system showed a higher value of flexural load than welding techniques, while the GFRP showed similar flexural load to welding techniques. Phase 4 involves assessment of FRP hybridization systems on bending behavior of joined metallic pipes. The improvement in the mechanical performance of pipes joined with four layers of hybrid FRP were found to be insignificant compared to four layers of non-hybrid FRP type. However, increasing the number of hybrid FRP layers to eight resulted in significant improvement in flexural loads compared to four layers of single FRP type. The overall results revealed that using FRP composites in pipes joining showing a promising future for the pipeline.
  • Nonlinear free and forced vibrations of porous sigmoid functionally graded
           plates on nonlinear elastic foundations
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): Xiao-Lin Huang, Lei Dong, Geng-Zhong Wei, De-Yue Zhong This paper focuses on the nonlinear free and forced vibrations of porous sigmoid functionally graded material plates resting on nonlinear elastic foundations. Two types of porosity distributions, even and uneven, were considered. A nonlinear three-parameter foundation model was employed to estimate the plate-foundation interactions. The material properties of the plates, described by the sigmoid distribution law, were assumed to be graded in the thickness direction. All four edges of the plates were simply supported and had no in-plane displacements. Based on a higher-order shear deformation plate theory and general von Kármán-type equation, the equations of motion with the effects of nonlinear elastic foundations were developed. The equations of motion were solved by an improved perturbation technique to determine the nonlinear frequencies and dynamic responses of the plates. The numerical illustrations are presented in both tabular and graphical forms to show the effects of the nonlinear foundation parameters, pore volume fraction, and material volume fraction on the nonlinear vibration and dynamic responses of the plates.
  • An analytical model for wood composite sandwich beams with a biaxial
           corrugated core under bending
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): Mostafa Mohammadabadi, Vikram Yadama, Lloyd Smith In this study, an analytical model to evaluate the bending behavior of wood-based sandwich panels with a biaxial corrugated core was developed. A homogenization method was adopted to replace the geometry of the core with a homogeneous medium. Considering the deformation of the core under pure tension, compression, and shear, the properties of the homogenized core were computed. A high-order sandwich panel theory, that takes into account the deformation of the sandwich beam through the thickness, was applied to derive the governing equations. Fourier series expansions were used to solve the governing equations for a simply supported sandwich beam. The analytical results for sandwich beams with two different geometries were compared to finite element predictions and experimental results. The analytical model differed by 0.5–1.9% from the finite element model, and 1.6–7.8% with experiment.
  • Retrofit scheme of FRP jacketing system for blast damage mitigation of
           non-ductile RC building frames
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): Jiuk Shin, Jong-Su Jeon Non-ductile reinforced concrete building structures built before the 1970s have been significantly damaged and collapsed under man-made disasters (e.g., blast loads) due to their inadequate column details. The structural deficiencies can be mitigated by a fiber-reinforced polymer jacketing system. This research investigated the blast performance of a low-rise non-ductile building frame strengthened with the jacketing system. Based on the investigation, a retrofit scheme was established to mitigate the blast-induced damage and maximize the effectiveness of the retrofit system. The retrofitted models varied with the main parameters of the retrofit system associated with the confinement effect and flexural stiffness, and blast simulation was performed under various loading scenarios. The retrofit effect was examined in terms of confinement and stiffness ratios. Since the effects of the retrofit parameters on the blast performance depend on the blast loads, the retrofit scheme needs to be established in terms of expected blast loading scenarios.
  • A method to predict the fatigue life and the residual strength of
           composite materials subjected to variable amplitude (VA) loadings
    • Abstract: Publication date: 15 November 2019Source: Composite Structures, Volume 228Author(s): Alberto D'Amore, Luigi Grassia A method to predict the fatigue life and residual strength of fiber reinforced composites subjected to variable amplitude (VA) loadings was developed. Based on a recent two-parameter residual strength model for constant amplitude (CA) loadings and coupled with the “equivalent residual strength assumption” (ERSA) the method allows accounting for the cycle-by-cycle loading variability and to build on a solid foundation a numerical procedure for fatigue calculations under spectrum loadings. The responses of quasi-isotropic carbon/epoxy laminate subjected to ordered and random block loadings were first tested and the simulations revealed that the load order strongly impacts residual strength. Then the approach is extended to a large database available in literature concerning the residual strength of E-glass/vinyl ester composite laminate subjected to ordered ascending (L-H) and descending (H-L) and random block spectra using a reference spectrum with of 735,641 cycle and 22 stress levels. It is shown that the predictions agree very well with experimental results including a series of premature failures that remained unpredicted before this study.
  • Effect of automated fiber placement (AFP) manufacturing signature on
           mechanical performance of composite structures
    • Abstract: Publication date: Available online 29 August 2019Source: Composite StructuresAuthor(s): Minh Hoang Nguyen, Avinkrishnan A. Vijayachandran, Paul Davidson, Damon Call, Dongyeon Lee, Anthony M. Waas A comprehensive and detailed experimental study of the influence of imperfections caused during Automated Fiber Placement (AFP) manufacturing is reported. Specimens with controlled gap and overlap imperfections of varying sizes and distribution were manufactured and tested. Pre-test microscopy inspection has been conducted to quantify the change in geometry due to compaction. Test results show significant knockdown in stiffness and strength due to gaps, specifically with larger gap sizes showing higher knockdown. Overlaps, on the other hand, may provide improvement in tensile properties and show negligible change in compressive properties. Digital image correction (DIC), in situ inspection with edge cameras and post-test microscopy analyses provide a detailed insight into the failure progression and modes.
  • Modeling Guided Wave Propagation in Multi-layered Anisotropic Composite
           Laminates by State-vector Formalism and the Legendre Polynomials
    • Abstract: Publication date: Available online 28 August 2019Source: Composite StructuresAuthor(s): Gao Jie, Lyu Yan, Zheng Mingfang, Liu Mingkun, Liu Hongye, Wu Bin, He Cunfu This research presents a numerical method to analyze the propagation characteristics of guided waves in multi-layered anisotropic composite laminates. The dispersion equations were derived theoretically, while the displacement and stress components of each layer are expressed in the form of state vectors, by combining the state-vector formalism and the Legendre polynomials (SVF-LP). The displacement fields are fitted approximately by Legendre polynomials, and the system of linear equations are constructed by the orthogonal projection. The eigenvalue/eigenvector solution is established to compute the phase dispersion curves instead of solving the transcendental dispersion equations. This overcomes the problem of missing roots in traditional matrix method effectively. In order to verify the robustness of the SVF-LP, three cases of multi-layered laminates, formed by isotropic material, unidirectional carbon-fiber epoxy prepreg and fiber-metal laminate (GLARE 3-3/2) are investigated, respectively. The influences of fiber angle change and the stacking sequence are primarily analyzed, on the dispersion characteristics and the displacement and stress profiles. The matrix method is also carried out to compare the accuracy of this proposed method, which is done by the commercial software Disperse. Finally, the displacement and stress profiles of fundamental modes of the guided waves in an arbitrary lay-up quasi-isotropic plate at a given frequency is discussed in details.
  • Influence of the tufting pattern on the formability of tufted
           multi-layered preforms
    • Abstract: Publication date: Available online 26 August 2019Source: Composite StructuresAuthor(s): Shen Hao, Peng Wang, Xavier Legrand, Lingshan Liu, Damien Soulat As a relatively novel technique, tufting is recently used to provide through-thickness reinforcement of a traditional 2D multi-layered preform, thus improving its resistance to delamination in the final part. In order to optimize the manufacturing process of the composite preforms reinforced by tufting, the studies of the forming behaviour of these tufted preforms are quite necessary, in particular, the influence of the tufting pattern. The present paper investigates the formability of the circle-spiral and square-spiral tufted preforms during the hemispherical and square-box forming. The forming defects and the consistency between the tufting pattern and punch shape are mainly discussed. The experimental assessment demonstrates that the tufting pattern has an impact on the formability of tufted preform and can modify/remove the forming defects. Moreover, there is no significant importance to use the similar tufting pattern to the punch shape and the forming results depend on the number of the tufting points in the zone underlying the blank holder.
  • Global Sensitivity Analysis of Piezoelectric Energy Harvesters
    • Abstract: Publication date: Available online 24 August 2019Source: Composite StructuresAuthor(s): Rabie Aloui, Walid Larbi, Mnaouar Chouchane Vibration energy harvesting using the direct effect of piezoelectricity has attracted increasing attention during the last two decades. Different modeling techniques have been applied to describe the electromechanical coupling effect of a piezoelectric harvester and to predict its electrical output. This study aims to identify the most important properties of both harvester substrate material and piezoelectric material that cause uncertainty in the predicted performances of the harvester. Global sensitivity analysis, applied in this paper, is a promising method used to identify systems parameters which have significant impact on the system output. In this paper, the Elementary Effects method (EEs), a particular implementation of the global sensitivity method, is used to identify the impact of substrate and piezoelectric material properties on the voltage frequency response function of a typical bimorph piezoelectric energy harvester with fixed geometry. With a small number of model evaluations at selected ranges of material properties, it has been found that the elastic modulus and density of the piezoelectric layer are the parameters which lead to the largest output variability. Furthermore, it has been found that the order of importance of the parameters can change from short-circuit to open-circuit conditions.
  • Multiscale modelling of thermoplastic woven fabric composites: From
           micromechanics to mesomechanics
    • Abstract: Publication date: Available online 22 August 2019Source: Composite StructuresAuthor(s): J.I. Múgica, C.S. Lopes, F. Naya, M. Herráez, V. Martínez, C. González The mechanical properties of woven composites can be predicted by using a multiscale modelling approach. The starting point to its application is the microscale (the level of fibres, matrix and interfaces), that allows the computation of the homogenised behaviour of the yarn. The aim of this work was to predict the yarn-level behaviour of a thermoplastic-based woven composite in order to allow the formulation of a representative constitutive model that can be used to predict ply properties at the mesoscale. To accomplish this purpose, an in-situ characterisation of the microconstituents was carried out. This served to generate inputs for three different representative volume element (RVE) models that allowed predicting the yarn longitudinal, transverse and shear responses. These mechanical characteristics allowed the determination of homogenised yarn constitutive behaviour which was found to be characterised by significant non-linearity until failure, specially in transverse and shear directions.
  • Electrical resistivity rresponse of unidirectional thin-ply carbon fiber
           reinforced polymers
    • Abstract: Publication date: Available online 22 August 2019Source: Composite StructuresAuthor(s): Hai-hong Wu, Shi-chao Li, Jin-na Zhang, Liyong Tong In this study, we investigate the effects of the thin-ply on electrical resistivity and its response to the tensile loading of carbon fiber reinforced polymers (CFRPs). Our results show that the resistivity in the thickness direction of the unidirectional laminate (UDL) made from thin-ply rises linearly at a small rate with the increase of the load until the load reaches 77.7% of the tensile strength calculated with the mix law of the composites, which is 1.43 times that of the thick-ply UDL. For thick-ply UDL, such linear response presents two phases. The resistivity increases at a small rate in the first stage in which the maximum load is low. The rate increased in the second stage is twice that of the first stage, and the threshold of the load corresponding to the stage is 54.4% of the tensile strength calculated with the mix law. It was found that the electrical resistivity of the CFRP in the thickness direction was related to the morphology of the resin-rich zone in between two plies and is less dependent of fiber volume fraction if fiber volume fraction is greater than a critical value in the composites.
  • Application of ANN in predicting ACC of SCFST column
    • Abstract: Publication date: Available online 20 August 2019Source: Composite StructuresAuthor(s): Viet-Linh Tran, Duc-Kien Thai, Seung-Eock Kim The main objective of this paper is to derive a new empirical formula for predicting the axial compression capacity (ACC) of square concrete-filled steel tubular (SCFST) columns using the artificial neural network (ANN). A total of 300 experimental data of SCFST columns extracted from the literature were used for training, testing, and validating the ANN models. The trial and error method was used to determine the best ANN model, which had the highest correlation coefficient (R) and the lowest mean square error (MSE). In addition, several existing and design code formulae were adopted to evaluate the performance of the current study. The comparative results revealed that the ANN model was more stable and accurate than any other existing formula. Using the validated ANN, a number of master curves were generated to establish a new formula to predict the ACC of the SCFST column. The comparisons with the existing formulae showed a higher accuracy of the proposed empirical formula.
  • Mesoscale Analysis on Ultra-High Performance Steel Fibre Reinforced
           Concrete Slabs under Contact Explosions
    • Abstract: Publication date: Available online 19 August 2019Source: Composite StructuresAuthor(s): Yun Peng, Chengqing Wu, Jun Li, Jian Liu, Xiangwei Liang This paper develops a more efficient and applicable three-dimensional mesoscale model to simulate ultra-high performance steel fibre reinforced concrete (UHP-SFRC) slabs under contact explosions. In the proposed mesoscale model, UHP-SFRC consists of two components involving concrete matrix and steel fibres. The straight steel fibres are randomly distributed and orientated in the concrete matrix using the self-coding program. The proposed mesoscale model is firstly validated with a series of static and dynamic tests, and then it is adopted in the numerical simulation of contact explosions. With the verified mesoscale model, parametric studies are conducted to investigate the effects of slab thickness and TNT charge weight on the crater damage of UHP-SFRC slabs under contact explosions. Based on the results of parametric studies, a damage identification multi-classifier is constructed to recognize and predict the damage of UHP-SFRC slabs under contact explosions by using the support vector machine (SVM).
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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Fax: +00 44 (0)131 4513327
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